Observer pattern implementation
Addition of an AbstractModel class
Creation of a classic key-word search model

+ Return type of getTweets() method modified
Modification of observers notifications

+ Observers now handle QueryResult objects instead of Strings
+ getTweets() method become search()
Addition of an AbstractController class
SearchController added
Addition of the query information into the controller
SearchView added
Main of the application added
Ajout élément de debug
UI modiications
Merge branch 'mvc-implementation' into develop