Fix signing out not cleaning up model data

TODO.md

@@ -10,7 +10,8 @@
 
 ## Issues
 
-- Signing out leaves the account's rooms in the list
+- Replying to one of our own message that's currently only a local echo
+  results in a reply to an empty ID
 - Need to unregister popups/menus when they are destroyed without being closed
 
 - Bottom focus line for an `HTextArea` inside a `ScrollView` is invisible,

src/backend/backend.py

@@ -198,8 +198,20 @@ class Backend:
         """Log a `MatrixClient` out and unregister it from our models."""
 
         client = self.clients.pop(user_id, None)
+
         if client:
             self.models["accounts"].pop(user_id, None)
+            self.models["matching_accounts"].pop(user_id, None)
+            self.models[user_id, "uploads"].clear()
+
+            for room_id in self.models[user_id, "rooms"]:
+                self.models["all_rooms"].pop(room_id, None)
+                self.models[user_id, room_id, "members"].clear()
+                self.models[user_id, room_id, "events"].clear()
+                self.models[user_id, room_id, "filtered_members"].clear()
+
+            self.models[user_id, "rooms"].clear()
+
             await client.logout()
 
         await self.saved_accounts.delete(user_id)