Full screen fixes (aspect ratio & IE11) and aspect ratio option

Full screen image now has correct aspect ratio
 - full screen root is now the parent of the canvas (required for Firefox)
 - canvas size is adapted via styles
 
Full screen now works properly in Internet Explorer 11.

It is now possible to optionally force a specific aspect ratio for the canvas
 - canvas size is adapted via styles
 - ratio for now has to be set manually in compiled JS (search for "// canvas.aspectRatio = 4 / 3;")

I'd much prefer the aspectRatio to be set earlier (in the source code or somewhere in the project). Any help on improving this would be much appreciated.

(This is my first pull request. I'm new to using Github actively. Please let me know if I made any mistakes.)