Integrate global planner with an updated controller

[mcdoerr]

To match the changes to the global planner, we have removed the halton points and integrated a path-following controller. The trajectory is chosen now by the cross-track-error, along-track-error, collision-cost, and heading-error to a lookahead point from the path published by the global planner in mushr_gp.

We have also added backwards rollouts to the trajectories considered in dispersion rollouts. This allows the car to follow the backwards paths sometimes generated by the global planner.

Finally, we have tuned parameters to fit the new controller, including the K number of rollouts for the dispersions.

[schmittlema]

This looks good!
Three things I noticed

1. If you place the goal directly behind the robot but facing the opposite direction the car will not turn around. The path incorporates turning around but the car ignores it
2. We could use more print statements. One right at startup that says "Initializing...." so that people know it is doing something. Another one for when we load a perm region from file. In case we need to delete it. This helped me with the last point below.
3. The map is set to "default", not the map name. I think there is a warning about this. This can cause a problem if you switch maps because the permissible region will be for the previous map (default.npy). Permissible region is the region where there are no obstacles, so if you use another map's region, then you will have some funky or failing behavior.