Ouya pause button support

Ouya system button sends Keycode.Menu after a delay if no double tap or hold is detected. It also sends Keycode.Home just before the system menu is opened (but not on dev kit controllers): http://forums.ouya.tv/discussion/comment/6076/#Comment_6076
Merge pull request #1585 from Aranda/ouya_menu_button

Ouya pause button support