Added subGrid return on getSubGrid method
Added toString()
Added getter to get the next piece a player has to put on the gameboard
Added method to get available pieces.
Added method to get current player turn.
Change parameter of onPiecePlaced from Piece to StateChangeListener to handle game state change and update view.
Removed ViewManager, useless class.
Update GameWindow according to deletion of ViewManager. (WIP)
GameView now knows the game controller to handle every input on the view.
Minor fixe : draw method throws now IOException if content loading fails
Changed way  to display Piece. GameboardComponent  handles mouse input right now. AvailablePieceComponent displays remaining pieces to put on gameboard
Added missing listener interfaces for QuartoView ...
Controller implementation. (WIP) has to manage playerturn and state changes.