Add a functionality of removing skeleton from world
Merge branch 'origin/master'

Conflicts:
	src/constraint/ConstraintDynamics.cpp
	src/dynamics/Joint.cpp
	src/dynamics/Joint.h
	src/dynamics/Skeleton.h
Fix updating mBodyIndexToSkelIndex in ConstraintDynamics::removeSkeleton()
Add functionality of spawning/deleting cubes for "cube" app
Merge branch 'origin/master'
Merge branch 'origin/master'

Conflicts:
	src/collision/CollisionDetector.cpp
	src/collision/CollisionDetector.h
	src/constraint/ConstraintDynamics.cpp
	src/constraint/ConstraintDynamics.h
Merge pull request #112 from dartsim/removing_skeleton_functionality

Add a functionality of removing skeleton from world