Unhide hidden (gradient, vector potential, ... ) files

[smiet]

Following the discussion in #208 , and not wanting to keep this valuable contribution hanging whilst this is resolved, I am opening an issue to discuss the unhiding of hidden output files.

The hidden files are:

Extension	Description	Originating Fortran File
.GF.ev	The eigenvalues and eigenvectors of the Hessian	hesian.f90
.GF.ma		hesian.f90
.sp.DF	Derivative matrix	newton.f90
.sp.A	Initial guess for vector potential	ra00a.f90
Commented out files
.poincare.0	Poincare or output file	newton.f90
.sp.t.0	rotational-transform data	newton.f90
.hessian.0	contains hessian matrix	hesian.f90
.GF.hocl1	Debugging	dfp200.f90
.GF.hocl2	Debugging	dfp200.f90

Reasons to keep them hidden that have been raised:

• No clutter in the workspace.
• Old runs will execute the same

Reasons for removal that were raised:

• Confusing to beginners
• (Hidden) stateful exection: if the file is present, and depending on when it was made, SPEC can either converge or get stuck)

@SRHudson @SHenneberg @jons-pf @jloizu @ErolBa