Removes bottom status bar.

StatusBar class calls are commented out and replaced with notifications.
SlicicingProgress notification shows progress of slicing, ProgressIndicator notification handles other progress information, like arrange objects etc.

src/slic3r/GUI/HintNotification.cpp

@@ -1012,7 +1012,7 @@ void NotificationManager::HintNotification::retrieve_data(bool new_hint/* = true
 	if(hint_data != nullptr)
     {
         NotificationData nd { NotificationType::DidYouKnowHint,
-						      NotificationLevel::RegularNotification,
+						      NotificationLevel::RegularNotificationLevel,
 							  0,
 						      hint_data->text,
 							  hint_data->hypertext, nullptr,