Update track fit EDM (#58)

### Briefly, what does this PR introduce?
This introduces changes to the track fit and track state EDM objects to
better conform to a single container that can deliver all of the needs
of downstream reconstruction algorithms and (ultimately) physics
analysis.

1. Introduces a 6D covariance matrix object that is really the upper
triangle of a full 6x6 covariance, for storage purposes.
2. Moves some "track level" quantities out from `edm4eic::Trajectory`
and into `edm4eic::Track`
3. Revamps the `edm4eic::TrackParameters` object, which will need to
contain the complete covariance to swap between edm4eic and Acts::EDM.
Also adds a surface type as bound track parameters make no sense without
an associated surface.
4. Adds a full covariance, position, and PID hypothesis to
`edm4eic::Track`

The resulting track object contains the set of track parameters at the
vertex, some criteria to evaluate the track fit (e.g. those contained in
the one to one relation to `edm4eic::Trajectory`), and all track states
associated to the fit (also still in `edm4eic::Trajectory`).

The track parameters at the vertex do need to be stored separately (e.g.
not as another uniquely defined track state), for a technical reason.
They are going to (1) be most frequently used in global coordinates,
which the track parameters are not in and (2) are associated to a
`PerigeeSurface`, which is transient unlike the surfaces associated with
the actual geometry. Without knowledge of the surface, a set of
BoundTrackParameters do not have a well defined global definition.

Opening this PR now as it will likely have nontrivial downstream
consequences, so comments welcome.

### What kind of change does this PR introduce?
- [ ] Bug fix (issue #__)
- [x] New feature (issue #__)
- [ ] Documentation update
- [ ] Other: __

### Please check if this PR fulfills the following:
- [ ] Tests for the changes have been added
- [ ] Documentation has been added / updated
- [x] Changes have been communicated to collaborators

### Does this PR introduce breaking changes? What changes might users
need to make to their code?
It introduces breaking changes to EICrecon. Currently there are 3
containers produced by the CKF in EICrecon - the aim of this PR is to
reduce this to a single container. This will in turn change other
downstream reconstruction algorithms that rely on the CKF output as they
will have to access this changed structure.

### Does this PR change default behavior?
No

edm4eic.yaml

@@ -135,6 +135,21 @@ components:
         }\n
       "
 
+  edm4eic::Cov6f:
+    Members:
+      - std::array<float, 21> covariance  // 6d triangular packed covariance matrix
+    ExtraCode:
+      declaration: "
+        Cov6f() : covariance{} {}\n
+        Cov6f(std::array<float, 21> vcov) : covariance{vcov}{}\n
+	float& operator()(unsigned i, unsigned j) {\n
+	  if(i > j) {\n
+	    std::swap(i, j);\n
+	    }\n
+	  return covariance[i + 1 + (j + 1) * (j) / 2 - 1];\n
+	}\n
+      "
+
   ## A point along a track
   edm4eic::TrackPoint:
     Members:
@@ -359,52 +374,47 @@ datatypes:
       - uint32_t          nMeasurements     // Number of hits used 
       - uint32_t          nOutliers         // Number of hits not considered 
       - uint32_t          nHoles            // Number of missing hits
-      - float             chi2              // Total chi2
-      - uint32_t          ndf               // Number of degrees of freedom
       - uint32_t          nSharedHits       // Number of shared hits with other trajectories
     VectorMembers:
       - float             measurementChi2   // Chi2 for each of the measurements
       - float             outlierChi2       // Chi2 for each of the outliers
     OneToManyRelations:
       - edm4eic::TrackParameters trackParameters // Associated track parameters, if any
-      - edm4eic::Measurement2D  measurementHits // Measurement hits used in this trajectory
-      - edm4eic::Measurement2D  outlierHits     // Outlier hits not used in this trajectory
 
   edm4eic::TrackParameters:
     Description: "ACTS Bound Track parameters"
-    Author: "W. Armstrong, S. Joosten"
+    Author: "W. Armstrong, S. Joosten, J. Osborn"
     Members:
-      - int32_t           type              // Type of track parameters (-1/seed, 0/head, ...)
-      - edm4hep::Vector2f loc               // 2D location on surface
-      - edm4eic::Cov2f    locError          // Covariance on loc
-      - float             theta             // Track polar angle [rad]
-      - float             phi               // Track azimuthal angle [rad]
-      - float             qOverP            // [e/GeV]
-      - edm4eic::Cov3f    momentumError     // Covariance on theta, phi and qOverP
-      - float             time              // Track time [ns]    
-      - float             timeError         // Error on the time
-      - float             charge            // Particle charge
-    OneToOneRelations:
-      - edm4eic::Trajectory trajectory      // Trajectory associated with these track parameters
+      - int32_t              type              // Type of track parameters (-1/seed, 0/head, ...)
+      - uint64_t             surface           // Surface for bound parameters (geometryID)
+      - edm4hep::Vector2f    loc               // 2D location on surface
+      - float                theta             // Track polar angle [rad]
+      - float                phi               // Track azimuthal angle [rad]
+      - float                qOverP            // [e/GeV]
+      - float                time              // Track time [ns] 
+      - int32_t              pdg               // pdg pid for these parameters
+      - edm4eic::Cov6f       covariance        // Full covariance in basis [l0,l1,theta,phi,q/p,t]
+
 
   edm4eic::Track:
     Description: "Track information at the vertex"
-    Author: "S. Joosten"
+    Author: "S. Joosten, J. Osborn"
     Members:
-      - int32_t           type              // Flag that defines the type of track
-      - float             chi2              // Total chi2 (sum) of the track fit
-      - int32_t           ndf               // Numbers of degrees of freedom of the track fit
-      - edm4hep::Vector3f momentum          // Track 3-momentum at the vertex [GeV]
-      - edm4eic::Cov3f    momentumError     // Covariance matrix on the momentum
-      - float             time              // Track time at the vertex [ns]
-      - float             timeError         // Error on the track vertex time
-      - float             charge            // Particle charge
+      - int32_t            type                           // Flag that defines the type of track
+      - edm4hep::Vector3f  position                       // Track 3-position at the vertex 
+      - edm4hep::Vector3f  momentum                       // Track 3-momentum at the vertex [GeV]
+      - edm4eic::Cov6f     positionMomentumCovariance     // Covariance matrix in basis [x,y,z,px,py,pz]
+      - float              time                           // Track time at the vertex [ns]
+      - float              timeError                      // Error on the track vertex time
+      - float              charge                         // Particle charge
+      - float              chi2                           // Total chi2
+      - uint32_t           ndf                            // Number of degrees of freedom
+      - int32_t            pdg                            // PDG particle ID hypothesis
     OneToOneRelations:
-      - edm4eic::Trajectory trajectory      // Trajectory of this track
-      - edm4eic::Vertex   vertex            // Track vertex of this track
+      - edm4eic::Trajectory                     trajectory      // Trajectory of this track
     OneToManyRelations:
-      - edm4eic::TrackerHit trackerHits     // Hits that were used for this track
-      - edm4eic::Track    tracks            // Tracks (segments) that have been combined to create this track
+      - edm4eic::Measurement2D measurements      // Measurements that were used for this track
+      - edm4eic::Track      tracks            // Tracks (segments) that have been combined to create this track
 
   edm4eic::TrackSegment:
     Description: "A track segment defined by one or more points along a track."