Blender Git Loki

2.5 - Restoring Bone Groups

* Added Bone Groups UI to 'Armature' context buttons for now. Later, it may be more convenient to have these with bones instead?

* Added operators for the operations that can be performed on these groups. Moved the core adding/removing functions to blenkernel so that they can be used elsewhere in future if need be.

* Properly wrapped bone groups in RNA. Copied the way that Vertex Groups are wrapped, since they share some similarities. Setting colours for bone groups still needs more work though.