Publication of Group Announcements

Groups have announcements to make that are not events - let's help people keep up with them as well.

We're talking news items that would otherwise be sent to mailing lists for example. Tickertape, and basically anything you'd like people to know that is not an event.

Use cases:
- Selwyn JCR have 50 free rape alarms to give away.
- Selywn porters want to notify their students that there's been a security breach on A Staircase.
- The Recorded Drama Society announces a script-writing competition, with a deadline 3 months in the future.
- TCS need a new editorial team to apply.
- SIFE Cambridge won an award at the competition they just attended and want to tell interested parties.