11/19 filled out some board fxns - John Marinelli

filled out:
Board::Board
Board::isSpaceEmpty
Board::getPieceOnSpace
Board::addPieceToBoard
Board::removePieceFromBoard

added public functions:
Board::addPiece (missing 1 error-checking capability)
Board::removePiece
Board::getIndexFrom2D (because Arraylist is 1D, we can use this function to compute the index we want given 2D coordinates)

also changed the 2D array to an ArrayList for l337 member functions