Add ShapeSphere.
Create collision detectior interface.
Add new fcl collition detector. (mesh and primitives)
Keep old fcl collision detector. (always mesh-mesh)
Merge branch 'origin/master'

Conflicts:
	src/robotics/World.cpp
Resolve complie errors.
Use mesh-mesh collision detection only in ConstraintDynamics.
Merge branch 'origin/master'
Merge branch 'origin/master'
Change minor things.
Merge branch 'origin/master'
Merge pull request #60 from dartsim/primitive_collision

Ready to support primitive geometries for collision