Initial integration

Initial updates to the original ArcMenu to support our app, but with an eye toward keeping it reusable and flexible. Key changes:
* Added IntelliJ project files.
* Added styleable attributes to ArcMenu.
* Menu items now fade in/out on expand/collapse so they don't peek out from behind the menu button.
* Added variant of addItem() that takes a drawable resource and auto-sets the button size accordingly.