Bullet sprite rendering

[viking-sudo-rm]

Should not programmatically rotate the sprites for bullets.

In this case, probably fine to not change the sprite based on the angle. But in general, for other sprite types, should not create a new copy of the sprite for each entity. Instead, we should maintain a static cache of sprites, and allow each entity to have a reference to one of these sprites.

[viking-sudo-rm]

In general, the old homemade animation stuff is sort of clunky.