…object

The new code mirror what is done in edit-as-Maya when the object transtions from being USD to being Maya. When it did, the UFE light proxy in Maya was deleted,  and the missing notification in merge-to-USD was preventing the proxy from being recreated.

- No longer send an explicit add notification for the item that was converted from Maya to USD.
- Call the parent function instead of the defaultParent function. We only need to invalidate the scene from the point where the object were edited.
- When calling defaultParent, the entire Maya cene would be invalidated.
- Change the implementation of the proxy shape default parent since it is a Maya node, its default parent must also be a Maya node.
- Fortunately, the old behavior was only used when reparenting and one cannot change the location of the USD virtual root, so the old bahavior was never used in  practice, as far as I can tell.

…a-usd into bailp/EMSUSD-190/lost-light