Right now, comparing dates with gcal_date_time_compare_date() gives
the exact opposite result of when comparing using g_date_time_compare().
As shown by this patch, this was a source of *many* bugs.
GObject automatically notifies when passing
properties as part of g_object_new(). This
happens after the instance is created, thus
after constructed().
By passing G_PARAM_EXPLICIT_NOTIFY, we avoid
this behavior. However, we are still notifying
PROP_CONTEXT in GcalWindow. Removing this other
notify fixes the crashes related to GcalContext.
https://gitlab.gnome.org/GNOME/gnome-calendar/issues/417