Working on module 4, just need to pass it off

LIST OF CHANGES:
-Chessboard's movePiece method now returns a boolean to indicate whether or not the move was successful, passes itself in to a Piece's validate move method so that Pawn can check if there are pieces around or in the way, and for later collision detection
-GameManager now has two Player objects, one controls white pieces and the other controls black pieces, runGame now keeps track of player turn and changes the player's turn after each successful turn
-Player now has constructor that allows one to pass in a boolean to determine whether it is white or not, and the takeTurn method now makes sure that the Player is moving its own pieces
-Pawn now has isValidFirstMove, which checks if its first move is valid. isValidMove now takes into account whether or not the Player tries to capture pieces diagonally, and makes sure that the Player can't capture a Piece directly in front of itself
-All Pieces now get a copy of the board for future implementations of collision detection