Redid the particle system a bit

-Subclasses for Particles are no longer necessary
-Instead, Particles take three arguments; an image and two functions
-Redid the Particles released by Blocks (and gave them color)
-Adapted the starfield to this new Particle constructor
-Removed Particle's knowledge of the ParticlePool that holds it
-Created ParticlePool.clean() in accordance
-config.get_colored_objects() can now make transparency optional