Button - bug fixes, issue phaserjs#1246

  - Fix incorrect passing of "was clicked" to processInteractiveObjects
  - Button would not return to Over/Out state because of strict too check to catch `undefined`
  - Removed [undocumented] property usage from processInteractiveObjects and slight reformatting
  - Update Button state frames/sounds to remove duplication
  - Updated documentation in Button for consistency

Author: pnstickne