Constants for reference of session's events

SessionCallbackEventCode – it is list of constants which refer to events in session.

UnknownEvent = 0 - event cannot be recognized;
Error = UnknownEvent + 1 - general error event;
Status_Error = Error + 1 - inner state session error event;
Execution_Error = Status_Error + 1 - execution session error event;
ItIsReadyToStart = Execution_Error + 1 - session ready to start event;
ItIsStarted = ItIsReadyToStart + 1 - session is started event;
ItIsPaused = ItIsStarted + 1 - session is paused event;
ItIsStopped = ItIsPaused + 1 - session is stopped event;
ItIsEnded = ItIsStopped + 1 - session is ended event;
ItIsClosed = ItIsEnded + 1 - session is closed and resources are released event;
VideoCaptureDeviceRemoved = ItIsClosed + 1 - lose connection to video source event.