Touch IE_handleEvent window scoped instead of canvas scoped

[mdondorp]

I found 2 issues with this the ui/Touch module.

When not clicking on a canvas this implementation returns:
if (e.srcElement != stage.canvas) { return; }
which returns false, therefor cancels bubbling, killing focus on a text element.

and in Touch.IE_enable we have window.addEventListener instead of canvas.addEventlistener.
This will hog all the touch events, resulting in no longer working dropdowns (native elements)

Tested on surface tab IE11.

In Touch.IE_handleEvent moving the
if (e.srcElement != stage.canvas) { return; } to the 2nd line of the function and adding true to the return statement fixes my problems.
if (e.srcElement != stage.canvas) { return true; }