Added mana and fire delay
Gave projectile an entity
Add mana regeneration
Make spell free to cast
Make fireblast a spell
Merge branch 'spells'

Conflicts:
	src/Fireblast.java
	src/GamePanel.java
	src/Spell.java
Add images for QuakeTower and ArcherTower
Change all int coordinates to doubles. Fix exception with no enemies in
proximity.
Cast position to int
Fix dx rounding problem
Basic collision detection for projectile
Add icespell image
Basic collision detection for projectile
Merge branch 'spells'
Add pathfinding helper method to Grid
Merge branch 'grid'