Removed the const qualifier on all the solve() functions

Removed the const qualifier on all the getPlanningContext() functions
Added a call to loadPlannerConfigurations() to the final getPlanningContext()
This allows changes in the ros parameters to take effect before solve()
The Planning Pipeline calls solve() by getting the context, and then context->sovle(),
NOT by calling the interface's solve() function. This is a work around to allow
on the fly updates of the parameters using the existing loadPlannerConfigurations() without altering
the plugin interface.