Improve notification management (#561)

* Don't notify for comment when mentioned

fix #505

* Don't save notification for remote users

fix #472

src/routes/comments.rs

@@ -62,7 +62,6 @@ pub fn create(
                 },
             )
             .expect("comments::create: insert error");
-            comm.notify(&*conn).expect("comments::create: notify error");
             let new_comment = comm
                 .create_activity(&rockets)
                 .expect("comments::create: activity error");
@@ -80,6 +79,8 @@ pub fn create(
                 .expect("comments::create: mention save error");
             }
 
+            comm.notify(&*conn).expect("comments::create: notify error");
+
             // federate
             let dest = User::one_by_instance(&*conn).expect("comments::create: dest error");
             let user_clone = user.clone();