SimpleSetup Improvements

Moved useful features from Lightning to SimpleSetup while I was making Lightning inherit from SS:

- New function to access a solution's planner name, corresponding to new feature https://github.com/ompl/ompl/pull/11
- Handle to set a custom optimization objective
- Formatting fix where ``last_status_`` should be camel case
- ``simplifySolution()`` debug output now tells user how many states where removed
I'd actually put this in ProblemDefinition only, and call it (I guess with one more indirection) from there.