Changed access to the members of the model in order to allow the use of both a GtkTreeIter and its path
The load_devices method returns a list of devices instead of settings a dictionary in the settings
The devices list is saved during the application closing
Added comments
The devices list is loaded only if the FILE_SETTINGS_DEVICES file exists
The devices list is saved only if there're devices to save, otherwise the FILE_SETTINGS_DEVICES file is deleted
Fixed Italian translation