🖖 Breakout rooms

[Ivansss]

Fix #981

[SystemKeeper]

Some comments:

• Switching is working very smoothly - I like it!
• I had a crash when switching:

  Assertion failed: (_internal->figCaptureSession == NULL), function -[AVCaptureVideoPreviewLayer attachToFigCaptureSession:]_block_invoke, file AVCaptureVideoPreviewLayer.m, line 1201.
  dyld4 config: DYLD_LIBRARY_PATH=/usr/lib/system/introspection DYLD_INSERT_LIBRARIES=/Developer/usr/lib/libBacktraceRecording.dylib:/Developer/usr/lib/libMainThreadChecker.dylib:/Developer/Library/PrivateFrameworks/DTDDISupport.framework/libViewDebuggerSupport.dylib
  

  This only happened once and I was not able to reproduce it again.
• When switching the old session is not ended? I switched between Room1 and Room2. So initially I joined in Room1 and then switched to Room2, but my last frame was still visible in Room1 and the status on the cell changed to "Failed to connect to...". Sometimes I wasn't able to establish a connection again after that, but that might be a problem of my test env.
• Sometimes the chat is not shown again after switching. Problem is, that there's still a '_chatViewControllersometimes, because the switch was too fast. Usingdispatch_afterlooks like the most reliable to me incallControllerDidJoinCall` (I'd go for 0.5, since the animation is 0.3).