GUAC-955: Add guacViewport directive which maintains content within the visible portion of the browser window, even if the browser magically scrolls itself.
GUAC-955: OSK should not cover visible display area.
GUAC-955: Add element module and guacScroll directive. Refactor guacFocus to element module. Use guacScroll to update menu scroll during drag.
Merge pull request #38 from glyptodon/fix-ipad-scroll

GUAC-955: Fix handling of scroll on iDevices