Show announcements in calendar

Announcements are currently only shown on the dashboard - this is not good. Probably they should be a subclass of the CalendarEvent themselves?

added part::backend part::frontend workflow::discussing labels

mentioned in issue #1015 (closed)

removed workflow::discussing label

mentioned in issue #1202

marked this issue as related to #1202

created branch 976-show-announcements-in-calendar to address this issue

mentioned in merge request !1772 (merged)

closed with merge request !1772 (merged)

mentioned in commit e55b186c