Initial Commit for making the time slider accessible. Changed it to be an anchor element for discoverability (READ: USE SEMANTIC MARKUP) and added in keyboard support. Gave the anchor the appropiate ARIA attributes and ROLE property for screen readers.

Also added a CSS class for offscreen text. Used this to add some offscreen text to discribe how to use the keyboard to seek the current video.
Merge remote-tracking branch 'origin/accessibility'