Turret Rotation, Little Dudes and Aesthetics

Added a second tank type to proof the modularity of the agent content.

Improved the particles to teach myself about using physics better in the particle system.

Custom texture for particles and trail render makes things look a little more finished, although the lasers are a little less clear.

SoundPlayer class now limits how many of each type of sounds can be playing at once, so you can actually hear the death explosions, albeit they are still very quiet for likely a multitude of reasons.