Create class for squares that have landed

Eventually can be used to replace STL vectors.
Add #define for square size
cSquare: accessors and mutators for top-left corner

In addition to setting/getting the center, you can also set/get the top
left corner.
Defines: tweak left and bottom limits

They should be exactly a multiple of |SQUARE_SIZE| from |GAME_AREA_RIGHT|,
|BLOCK_START_X|, and |BLOCK_START_Y|.
Replace STL vector with static arrays in LandedSquares