Implement turns. Change animation for BoardLocation.

Now a single enum represents the "colours" of the board. There aren't
separate enums for BoardLocations, ChessPieces or player turns. They all
use the same enum which has two values: white and black.

Changed the animation implementation from VisualStates to Triggers.

Implemented turns. Now only white pieces can be moved at the beginning.
Upon moving a piece the turn changes and only pieces of that player can be
selected and moved.