Model and controller

@bsoetaer 
Test by opening irb and creating a new CLIClient.  Use start and quit to start a new game or exit the program, and select a column to play by entering the zero-based column number.
Should also be cancelling if all board is full, i.e. totalTokens == board.height * board.width. Not sure how often this will happen with a full size board but it is important I think.