Dazzle is very sensitive to returning empty search results,
and ends up flickering when we pass a search model that is
not yet populated.
Wait for a few results, or for 150ms, before returning the
model.
https://gitlab.gnome.org/GNOME/gnome-calendar/issues/468
This is architectured in such a way that it will
allow us to introduce other searcheable terms in
the future.
All the functionality that in the past was in
GcalManager is now spread across GcalSearchModel,
GcalSearchHitEvent and GcalSearchEngine.