Added a new class to manage the dimensions of the Mesh Editor's grid.
Created a new class to manage the grid graphics and hooked the Mesh
Editor up to its GridDimensions.
Migrated the jME graphics for the grid to the class GridGraphics.
Implemented refresh for the GridGraphics. Removed old code from init.
Added documentation to GridDimensions and refactored one of its methods.
Also fixed a bug with the GridGraphics' custom mesh (the black
"background").