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.
Actually, I think the units are vestigial, left over from when we set the flags at the unit level. The tests only assert the flags are set at the service level, so I'll try removing this setup code. We have other unit tests elsewhere that make sure flags set on the service percolate down to all the units.