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.
The old code sent a database change event for every unit. It sent one event to the topology (which updated service view), but multiple change events on the DB (which updated machine view). As I mentioned elsewhere, I'm not sure we can aggregate up changes since machine view expects events to be specific to a particular unit or machine.