renamed WoodenCrate class to WoodCrate.  beginning to move crates out into their own classes.  each crate now has it's own sprite pool.  would like to figure out a more generic way to create them through their base class.
modified the cleaner() method to recycle a sprite into it's respective sprite pool
modified CrateThumbnail to crate the subclasses instead of just Crate().  This is where I'd like to be able to call something to the effect of Crate(type) and get back the correct subtype.  More on this to come.