Fail fast if a blank symbol is played
Implement GameBoard part of the display logic
Merge remote-tracking branch 'origin/ben_frankie_antonio' into ben_frankie_antonio

Conflicts:
	android-tic-tac-toe-core/src/main/java/com/novoda/calisthenics/tictactoe/GameBoard.java
	android-tic-tac-toe-core/src/test/java/com/novoda/calisthenics/tictactoe/GameBoardShould.java