Merge the accessibility fixes from master into the 2.1.x branch aswell.

This fixes a bug where the user couldn't select other buttons than "pause" when playing. This occurred because on every "timeupdate" event, the "pause" button was focus()'ed again.

I know there's a lot of weird commits here, but it shouldn't matter since we'll merge 2.1.x into master anyway later. Fixes [NOTA-237](https://notalib.atlassian.net/browse/NOTA-237)