recorder: refactor pipeline

Moves the recorder up one level to the VideoInput, VideoReceiveThread
and AudioReceiveThread, instead of the MediaDecoder (there's no
equivalent to the VideoInput in the audio layer).

Emits the RecordPlaybackStopped when the recording is stopped, so the
client can sync its recording state with the daemon, in case the daemon
stops recording by itself (rather than user intervention).

Change-Id: I743b080cb354273ec074fec51caf2a4328fc1c58