Let the canvas's container have bouncy webkit scroll,
disable pinch-to-zoom on the editor and viewer.
Fix toolbar positioning on body scroll.

When, after clicking in the text, the iOS keyboard
pops up, the entire editor body is scrolled upwards
because the window is shrunk, even if there was
no way to scroll it before.
This means that the toolbar slides upwards and out
of the visible part of the viewport.

This is unacceptable, therefore this commit introduces
a fix:
CSS-translate the toolbar when detecting a scroll. focusout,
or touchmove event.
Toolbar polish:

* Make the toolbar absolutely positioned and full-width.
This should let it's contents properly reflow when the
screen is not wide enough.
* Add a little shadow.
Make canvasContainer dodge the overlapping toolbar.
Editor: Remove window event listeners on destroy().
Merge pull request #356 from adityab/ui-nozoom

Some polish with iOS zoom and pan