IE11 fullscreen fix

[lbayliss]

Fixes the fullscreen buttons for IE11, which has its own set of prefixes:

• Entering fullscreen
• Fullscreen change event
• Exiting fullscreen

IE versions before and after 11 shouldn't be affected.

[pindiespace]

IE 11 is pretty well-behaved. I used a polyfill to handle this in my own fork.