Allow institutional admins to add Announcements about new things

[firasm]

It would be great if we could have a similar "news" thing for PrairieTest, in particular, something that will announce updates/changes for the CBTF that term.

Here are some use-cases:

1. New room is available

2. Policy change calculators

3. Expanded hours of operation

4. Student consent form for research study

I am running a study in the CBTF and I need an easy way to get consent for data collection and analysis for all courses without having to ask each course instructor to post a message to their students each term