Change Return Type From NSMutableArray To NSArray

Change return type from NSMutableArray to NSArray because have the
function has added to NSMutableArray. The array should not change much
outside of the function.
Change Clear Board In Chess Board Class

Change Clear Board function in Chess Board class to be dynamic and
allow either White or Black to be at the bottom of the chess board
meaning that it is what the user has selected. This is because later on
the user will have the option of choose a which colour to selected.