This prevent user from prematurely seeking the video.

This will fix the problem when user trying to click the seek button on
the iOS, as the video need to be started first before it can be
seekable.

iOS devices has a restriction that user has to click on the video
element to initiate playback. By visually disable the button, user will
be forced to click on the video itself, and everything will be worked as
expected.

Fixes https://www.pivotaltracker.com/story/show/30334381

This will make sure that the play button is in the paused state.

Fixes https://www.pivotaltracker.com/story/show/26236143