Ensure ThreadDelete only deletes owned Threads

[carsonfarmer]

Ideally, ThreadDelete should be tied to the identity of the peer that created it on a given peer in the first place, be that via CreateThread or AddThread. For now, if we assume that only 'owned' Threads can be delete by a remote peer, we save ourselves from allowing a remote client to delete a thread out from under another peer with a log in the same thread.