IMS: IMS fixes for conference

- Set phoneaccount in IMS conference object
- Add support conferencing connections after SRVCC
- Use user entity to remove participant
- IMS Conference Creation update
- Fix NPE in conference participants update
- Properly disconnect conf participants missing from list
- Use UserEntity to display Conf Participants
- Set the participants to disconnected state before
removing
- Handle conference call in DIALING state

Change-Id: Iac8ef26022ee8bbe95541e1a63509b1934e2965f
Bug: 21376607
4 files changed