Inherit from abstract Controller

The UI now expects an instance of a Controller, which is an abstract
base class. Our old Controller class has been renamed to ModOrganizer,
and it now also inherits from Controller.

This will allow us to define an interface that all of ModOrganizer, the
UI, and a yet-to-come FomodController can agree on.

ammo/ammo.py

@@ -2,7 +2,7 @@
 import sys
 from pathlib import Path
 from .ui import UI
-from .controller import Controller
+from .mod_organizer import ModOrganizer
 from .game import Game
 
 IDS = {
@@ -83,7 +83,7 @@ def main():
     )
 
     # Create an instance of the controller.
-    controller = Controller(DOWNLOADS, game)
+    controller = ModOrganizer(DOWNLOADS, game)
 
     # Run the UI against the controller.
     ui = UI(controller)