Modified package structure to make world classes easier to find. Removed
parametric Entity constructors and replaced with a setParams method.
Moved unit testing default parameters to EntityTestCase and reworked all
Entity unit tests to be more concise. Moved all Entity unit testing over
to MockSprite and removed DefaultSprites from current use.
Removed world.entity.base package and moved contents one level up, to
world.entity.
Added placeholder for GrassSprite, RoadSprite, TreeSprite pointing at
the default texture.
Merge pull request #36 from BU-CS673/Aaron

Aaron