Switch from events to setting service flags.

Instead of firing events on the topology, we're switching to setting
flags on the service and unit models in the DB. That way the data is
persistent across state changes (i.e., when a user switches from
service view to machine view) and we maintain one single source of
truth.
I think I preferred the old approach better where you updated them all then sent a single change event. The whole reason we use LML for units is because there may be 1000s. Reviving them all and sending 1000s of events is not very scalable.