Add a fullscreen button

[bpierre]

Gecko: https://wiki.mozilla.org/Gecko:FullScreenAPI
Webkit: http://peter.sh/2011/01/javascript-full-screen-api-navigation-timing-and-repeating-css-gradients/

[bpierre]

http://blog.pearce.org.nz/2011/11/firefoxs-html-full-screen-api-enabled.html