Add frontend-based announcement management

We want to support to add announcements graphically for following content types: Person, Group, ...

changed milestone to %2.0a2

added part::frontend type::feature workflow::discussing labels

assigned to @hansegucker

changed the description

Please add needed models in the description above, @all.

created branch feature/frontend-based-announcement-management to address this issue

mentioned in merge request !173 (merged)

added workflow::confirmed label and removed workflow::discussing label

closed via merge request !173 (merged)

mentioned in commit 70469506