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.
with no default it's undefined which is essentially false :) I would just prefer it to be explicit. By default all services are shown so they should all be false