Changed the metaplanners to only catch PlanningErrors instead of all Exceptions.
Changed the metaplanners to only catch PlanningErrors instead of all Exceptions.

This allows client code to actually catch and inspect unexpected errors thrown
from planners, at the expense of being less robust to strange error conditions.
Since these error conditions should be identified and fixed or handled anyway,
this seems more desirable than the previous blanket exception catching strategy.

Stefanos19/prpy,personalrobotics/prpy,cdellin/prpy