New Allies [Alpha 5]

This update adds ally versions of the slider, bullet, and trap elements. This is in preparation for an element that will be able to switch allegiance of elements - requiring total symmetry between the enemies and allies.

Endless mode has also changed: Only two doors in a newly opened room will advance the level (down from three). This should increase the challenge.

Fixes:

• Edit mode palette cursor can scroll now.
• Directions were not being added to various elements in Endless.
• Wall-elements were generating pathing information - causing enemies to chase allies they can't harm. Wall-elements no longer generate paths.
• Bullets were not dying when hitting indestructible elements.
• Slow elements were resetting their direction when changing state.