Merge pull request #84 from 4950/god

Projectiles tracked from center of spatials now.
Basic Round system. Monsters spawn in waves. Killing all monsters triggers next wave. Monster numbers increase and hp/damage scales. Player scaling not implemented yet.
Some code cleanup. Removed duplicate GameLogicSystem(two were being added to the same world)
Resource manager can now accept abstract resources with the Add method. Use this to manage resources not created by the ContentManager. Look in Dirty init for examples.
Movement now uses a psuedo-stack so that when you press more than one key, then let go of some, you don't just stop moving. It is now super smooth :D