Move Who's Turn It Is To Chess Board Class

Move who's turn it is to Chess Board class from asimplechessgame class
because the players turn is a basic chess function that and thus it
should actually be in the Chess Board class since this is the class for
all basic functions of a chess game. Also add in a property in order to
know if any of the players are in check for their next turn.
Merge Duplicated Set Chess Piece In Chess Board

Merge duplicated set chess piece functions together in chess board
class because they were doing the same thing the only different was
that one did not return anything. Also, now that setCellState is the
public, this can be used when promoting pawns if they reach the other
side of the board.