callmodel: reintroduce old signals to avoid race conditions during call
callmodel: reintroduce old signals to avoid race conditions during call

- Fixes a possibly null call object preventing the emission of
  remotePreviewStarted and resulting in no distant renderer
- This is only until the win32/macOS clients migrate completely
  to AVModel

Change-Id: I167ca480739664a14aac4da0f1dc16d8e18623b6

savoirfairelinux/ring-lrc,savoirfairelinux/ring-lrc,savoirfairelinux/ring-lrc,savoirfairelinux/ring-lrc,savoirfairelinux/ring-lrc