Currently dismissed events will simply reappear when browsing
back and forth between dates, which is clearly broken. Instead,
hide events that have been dismissed permanently. For now, we
simply store a list of ignored IDs ourselves, until we get API
in evolution-data-server to reliably store custom per-event
properties.
https://bugzilla.gnome.org/show_bug.cgi?id=744927
777616d8b0