[easy] Fix comment on GameTransitionsTest.js
Fix MAX_CELL_VAL to be 15
Use OFFSET_PER_TILE constant instead of hard coding 4
Consolidate GRID_SIZE in Grid.SIZE
Use Grid.CELLS_PER_STATE instead of 8, factor out _getOffset
Use static access instead of this._getOffset
insertTile to incrementTile
Add GameTransitions.visualize
Update GameTransitions.move to handle merging, plus tests