Delete notifications when deleting comments (#499)

* Implement find_for_comment for notifications

* Delete notifications when deleting a comment

This should tackle #463

* Apply rustfmt

* Implement `find_for_mention` and remove order by from `find_for_comment`

There is no need to order the notifications

* Delete notifications for mentions

* Fix notifications for comments and mentions

plume-models/src/comments.rs

@@ -330,9 +330,17 @@ impl<'a> Deletable<Connection, Delete> for Comment {
         act.object_props
             .set_to_link_vec(vec![Id::new(PUBLIC_VISIBILTY)])?;
 
-        for m in Mention::list_for_comment(&conn, self.id)? {
+        for m in Mention::list_for_comment(conn, self.id)? {
+            for n in Notification::find_for_mention(conn, &m)? {
+                n.delete(conn)?;
+            }
             m.delete(conn)?;
         }
+
+        for n in Notification::find_for_comment(conn, &self)? {
+            n.delete(conn)?;
+        }
+
         diesel::update(comments::table)
             .filter(comments::in_response_to_id.eq(self.id))
             .set(comments::in_response_to_id.eq(self.in_response_to_id))