Broadcast activities to all known instances

We consider everything posted with Plume public (for the moment at least)

plume-models/src/users.rs

@@ -100,6 +100,12 @@ impl User {
     find_by!(users, find_by_name, username as String, instance_id as i32);
     find_by!(users, find_by_ap_url, ap_url as String);
 
+    pub fn one_by_instance(&self, conn: &PgConnection) -> Vec<User> {
+        users::table.distinct_on(users::instance_id)
+            .get_results::<User>(conn)
+            .expect("Error in User::on_by_instance")
+    }
+
     pub fn delete(&self, conn: &PgConnection) {
         diesel::delete(self).execute(conn).expect("Couldn't remove user from DB");
     }