Demo app using UIPopoverController+Hack

Implemented a category for UIPopoverController that overrides the
private implementation of _popoversDisabled.

For more information, read Mark Sands’ article about “How Apple Cheats”
on http://marksands.github.io/2014/05/27/how-apple-cheats.html

This is for demonstration purpose. The best approach is change the
implementation using Method Swizzling.

Also, this probably won’t be accepted by Private API auto validation
when submitting binary to AppStore. For Enterprise distribution must be
fine.