Removal of the tweetPool
AppController now asks to the model to save the tweet pool when the application window is closed
AppModel doesn't write in CSV file anymore. At save, it just created Tweet objects corresponding to the Status and add it to its TweetPool.
When the window of the application is closed, the AppModel asks to its TweetPool to write the CSV file
Tweet is correctly build from a Status object : only the name of the user is saved in the filed 'twittos'
Addition of the possibility to set a message of a tweet to clear its message
Addition of a method to write a CSV file from the TweetPool contents
Delegate the addition of an element in the TweetPool to its internal hash map
When the window of the application is closed, the view asks to the controller to save the tweets the user wants to save