Finally beginning work on module 6, piece obstruction now fully implemented and working correctly after testing

GIGANTIC LIST OF CHANGES:
-Piece now has another abstract method called 'isMoveObstructed' which most pieces implement, excluding knight and king
-ALL obstruction logic implemented in Pawn, Queen, Rook, and Bishop, and fully tested with the 'obstructionTest' text file that was recently added
-Knight and King just return false when they implement their 'isMoveObstructed' method since Knight just doesn't GAF and King can only move one space, which is already accounted for in its 'isValidMove' method
-Small, but dumb note added to 'isKingInCheck' method in GameManager
-Deleted 'isPieceObstructed' method in Chessboard since a version of it is already implemented in each piece, also added a check for a piece being obstructed in the 'detectCheck' method
-'bishopTest' text file added for early bishop obstruction testing, and 'piecePlacement' text file also added to use from now on to place pieces on the board at the start of the game