Make atelet / ateom use actor UID for its internal bookkeeping

[juli4n]

Today we use the (atespace,name) tuple, but now that we have a server-assigned UID per actor, we should consider switching to using it. This will prevent issues when an actor is deleted and recreated with same name, within the same atespace.

[ericdbishop]

I've begun working on a PR for this 😃