Merge pull request #6 from BU-CS673/graphics

Initial structure for graphics subsystem, and basic prototyping of several basic game classes.
Created Damageable interface.
Merge pull request #12 from BU-CS673/graphics

Graphics - Many graphics system updates; added libgdx libraries; added temp tank texture
First mockups of basic game classes (Entity, Terrain, etc.). No unit
tests yet.
Fixed merge conflicts with changes to DrawableEntities.
Added Drawable interface, templates for Grass, Road, and Tree classes,
and outlined many Entity methods.
Created DummyEntity class for Entity unit testing to avoid OpenGL
conflicts. Added unit tests for Entity class.
Fixed bug in Tank constructor, rewrote Tank tests to include texture
loading.
Added javadoc comments to many Entity and subclass methods.
Added TODO comments to many classes.
Moved Entity matches() method to test class. Removed null checks from
Entity sublcasses implementing Drawable.
Merge pull request #16 from BU-CS673/Aaron

Outlined basic structure for Entity and many subclasses. Created Drawable and Damageable interfaces for Entities. Added test for Entities and Tanks. 16/16 Tests passed.
Merge pull request #19 from BU-CS673/production

Production -> Graphics