Remove -video suffix from youtube namespace functions.

It seemed redundant to be typing youtube/play-video and so on.
Add youtube/seek.
Add status and error handlers for Youtube player.

The handler methods don't actually perform any logic yet; consider them
hooks upon which to build further functionality. Right now the paused
and playing states have no-op handlers.
While video is playing, continuously place timecodes in channel.

While playback is in progress, an interval function will be called every
youtube/timecode-frequency milliseconds to place the current playback
timecode in the youtube/timecodes channel.