HolyOrders should not start when it's already running

[crantila]

Problem: HolyOrders is set to start according to a systemd timer. It's possible for a single HolyOrders run to take so long that the following execution begins before the first has finished. This would lead to a lot of unnecessary computation and would also potentially corrupt the update time database or produce errors because HolyOrders is not designed for that.

Solution: When HolyOrders starts, it should check whether another HolyOrders instance is already running. If so, the second HolyOrders instance should exit.