canvas-animation: Listen to 'input' events instead of 'change'.
canvas-animation:  Move GroupView instantiation after load from localStorage.

Instantiation of the GroupView before load results in its ObjectView
referencing a deleted model.
canvas-animation: Rerender GroupView's ObjectView if model was removed or is at a different index.

Protects against the ObjectView having a reference to a deleted model.
canvas-animation: Allow saving of empty groups.

This will set the editor to initial testing state if all objects are
removed..
canvas-animation: Only save to localStorage if modified.

If the current collection is the same as the last saved collection, it
is not necessary to save it again (multiple copies of same state).