Additional changes for Conference.

1) Connection.setConference() checked to see if the conference was valid
before setting it.  This prevented us from populating child connections
on a new conference until it was added.  Now we allow it but dont sent
the update unless the conference has already been sent.
2) removed unnecessary ArrayList<>() wrappers on CopyOnWriteLists.
3) Updated disconnect/hold/unhold so that they are sent to Conference
objects as well as Connection objects.
4) Added support for separating a child conference call.
5) Additional Logging

Bug: 15621105
Bug: 17136172
Change-Id: I939c36bc9694b9d81f0ff582e2fbe335006aa485