SetDeepEnabled

Commit message:

    Added UIElement methods SetDeepEnabled / ResetDeepEnabled / IsDeepEnabled to allow setting enable on an element + all its child elements / reset it to previous state.
    
    Example usage: On scroll view, could disable all children while touch-scrolling to prevent accidental triggering of items.

I probably didn't get the scripting thing right-- I didn't see where the similar UIElement methods were.

I've got a follow up pull-request for scroll view to do as in the example, if this is accepted.