Ready to support primitive geometries for collision

- CollisionNode and CollisionDetector are collision detection interfaces in DART.
- FCLMESHCollisionDetector is a concrete collision detector class uses FCL with mesh only (our old version).
- FCLCollisionDetector is a concrete collision detector class uses FCL with primitive geometries and mesh. Currently, FCLCollisionDetector is now working.

This pull request suggests
1. a new interface for multiple use of collision detection libraries
2. a first step for supporting primitive geometries for collision

If we don't need to support multiple collision detection libraries, then this feature can be removed.