turn core.Async from class to namespace
use core.Async.destroyAll for Editor.destroy
Merge pull request #469 from kossebau/makeCoreAsyncANamespace

Make core.Async a namespace
Add fullscreen and presentation support for IE11.

This amazing browser does camelCasing differently
for event names and also does not support the
isFullscreen or msIsFullscreen property on document.

Therefore this commit keeps track of the fullscreen
state with a custom flag, instead of asking the browser
for it.