Added functions pass and end_game in game.js and game_controller to handle passing.
Added button in game/start view to pass.
Added a route to game/pass.
Changed the way cell position is computed in submit_word to handle indices with more than a digit.
Changed the way to update and save attributes in Game and Player models, using update_attribute.
Added some tests for Game model.
Changed the name of the player created during the tests for Player model to avoid having the same name as a player in fixtures.