TickUntilCompletion() is now a static method and again takes an ApplianceAction parameter. It does a null check on each while iteration to handle the case where another thread nulls the action. Also added Run() method to ApplianceAction which initialises the ticker (now a private method), and let child classes call Run() instead.
For other actions we get a ticking timer in the Events view because they use PollToCompletion, which calls their Changed event every 900ms. These actions don't use PollToCompletion, and didn't regularly call their Changed event - so their timer didn't tick regularly. This change adds a lightweight mechanism to call their changed event every 900ms until they complete. This allows the events page timer to tick every second in the same way as it does for other actions.
