Expose each OMPL planner as a separate OpenRAVE planner

I modified or_ompl to create a separate OpenRAVE planner for each wrapped OMPL planner. This replaces the ability to specify the planner name in the `PlannerParameters` struct. E.g. there is an `OMPL_RRTConnect` planner that calls RRT-Connect and an `OMPL_PRM` planner that calls PRM. Both of these planners show up in `openrave --listplugins`.

I also added a `GetParameters` command that returns the list of supported parameters.
Oops, sorry! Still getting used to GitHub's diff layout.