Added TicTacToe in Samples

Here's just one more sample — a tic tac toe game! 

It runs easily with `jruby -J-XstartOnFirstThread shoes4/bin/ruby-shoes shoes4/samples/simple-tictactoe.rb`.
Interesting comment. Any chance you can duplicate the lack of centering in a smaller app, maybe just with a button in it? If so, would be great to get an issue logged for it!