Title Screen state & Collision kickback

- Caleb's "Nothingness" animated screen has been added (currently it contains way too many images)
- Tanis's theme song added
- hero now "bounces" backward upon collision with Maniacs and Loafers (not for Thugs)
- enemies have a slight kickback after being hit with the melee attack
- All of the kickback code was implemented inside the hero's checkAttack() subroutine 
- added a getClosestEnemy() method that returns the nearest enemy