Remove obsolete MediaEvent. Update more comments.
PARB feedback: Refactor SeekEvent.
PARB feedback: Merge ISwitchable event types into one event class.
More comment updates.
PARB feedback: Merge IAudible events into one event class.
Update some comments.
PARB feedback: Rename ViewChangeEvent to ViewEvent.
PARB feedback: Rename DimensionChangeEvent to DimensionEvent.
PARB feedback: Rename TraitsChangeEvent to MediaElementEvent.
