Working on adding PlanetPhysicsEvaluator

Have started pulling what I believe are the relevant methods from
PlanetPhysicsHelper to PlanetPhysicsEvaluator.
Continuing to add stuff to PlanetPhysicsEvaluator
Accessor for composition
Should be done porting to PlanetPhysicsEvaluator

Now to have the PlanetPhysicsHelper make everything available
that's needed by the PlanetPhysicsEvaluator.