Fixed the reference to be the point between the two wheels, not the
left wheel of the robot (top-left point). I thought that was changed a
while ago, but I botched one of the merges. That error would explain
  the robots still colliding occasionally. I made the point between the
  wheels act as the center - the actual center is only a few inches
  back so it should be okay if the radius is large enough.
Fixed a bug where the obstacle robot's goal configuration was not
converted to world coordinates before being pushed onto the path. This
made trajectories when the motion type was None.
Cleaned up collision detection class, added the buildTrajectoryRequest
function to utility in trajectory_evaluation. I will copy over the
method from ramp_planner when I work on it some more.