Implemented autopause modes (gh-784)

Added a pretty ugly dropdown to change the modes.  We need some real
styling for this.

Implemented PlaybackModeController to handle the dropdown and
autopause the video as needed.

Updated the mock VideoPlayer service so it can simulate
pause/play/seeking better.  Added mock $timeout service.
Only use auto-pause modes when in the typing stage.

Moved the selectbox to the workflow section, since it's tied to the
typing stage.

Updated the PlaybackModeController so the current mode is exposed.
This makes it more easily testable.