ReleaseAnnouncement provider, model and controller
Fix destructive helper method
Stub release announcements visible on frontend
Release announcement organisations are objects
Announcements can be filtered (rummager stubbed)
use real examples in rummager stub
1st pass at styling release announcements index
Add Upcoming Calendar tab menu to statistics index

This is a bit hacky at the moment.  The idea is to eventually
split out statistics into it's own site section living under
/statistics, but that is too hairy a job for now.
Frontend::ReleaseAnnouncement -> StatisticalReleaseAnnouncement

(rename)