Automatically updating CollisionGroups when ShapeNodes are added/removed

[mxgrey]

1. Currently a CollisionGroup will only pay attention to the ShapeNodes on a BodyNode or Skeleton that are present at the moment that they are handed over. It would be good if they could update automatically whenever the ShapeNodes are altered in some way. We could possibly do this with a wrapper class or build the functionality into CollisionGroup itself.
2. CollisionGroup currently does not know when a ShapeFrame it refers to gets destroyed. This can leave the CollisionGroup in an undefined state and lead to undesirable behavior.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you for your contributions.

[jslee02]

I believe this is resolved by #1112