Support video calls

resources/icons/ui/video-call.png

resources/qml/ActiveCallBar.qml

resources/qml/TimelineView.qml

resources/qml/VideoCall.qml

resources/res.qrc

src/CallManager.cpp

src/CallManager.h

src/ChatPage.cpp

src/UserSettingsPage.cpp

src/UserSettingsPage.h

src/WebRTCSession.cpp

src/WebRTCSession.h

src/dialogs/AcceptCall.cpp

src/dialogs/AcceptCall.h

src/dialogs/PlaceCall.cpp

src/dialogs/PlaceCall.h

src/timeline/TimelineViewManager.cpp

src/timeline/TimelineViewManager.h