Simplify our Fullscreen code

[ranyefet]

Our current Fullscreen code is quite bad. I suggest we move the fullscreen code into separate files which will handle all fullscreen code.

That file will use screenfull.js https://github.com/sindresorhus/screenfull.js/ behind the scenes and will have fallback to DOM resize.

[mdale]

does it also support friendly iframe expansion?

[mdale]

we should also look at cross-domain fullscreen. we should call dom fullscreen on the outer div.. not the outer iframe. i.e so that if the allowFullscreen attribute is set we can still enter dom fullscureen on thouse cross domain included iframes