Update: Jump 'n Bump 'n stuff

What's new:

• Player 3 and 4 can also be controlled with gamepads.
• Players can kill each other by landing on each other (yes, we're huge Jump 'n Bump fans).
• Better object placement UX: no more collisions with safe zones and diamonds while in placement mode, instead a red color overlay will show invalid placements (at the moment only safe zones; since TNT has been implemented, players can now place hazards like sawblades on diamonds)
• Bugfix: it was possible to kill a player while they're in placement mode; placement mode now makes players invincible.