New club announcements PR (and some other things added in)

[alanzhu0]

Building off #1617

[alanzhu0]

If you want to contribute to this PR, ask me for push access to the branch or rebase off this branch on your own fork.

[shrysjain]

Club announcements features left to add:

• Archive
• Search
• Restrict subscriptions for restricted activities to only those on the authorized list

[alanzhu0]

Also (small things):

• Automatically subscribe the club's sponsors to the club's announcements on save
• For this text on the request post page: "Want to post an announcement for your club's members? Submit a club announcement instead!" add it for club sponsors as well (currently only for club officers).
• Remove the homecoming banner from the club announcements page.
• Rewrite intranet/apps/eighth/views/activities.py, lines 60-64 and intranet/templates/eighth/take_attendance.html, line 500 to allow both the eighth activity sponsors and the club announcements sponsors to edit settings.
• For our initial beta rollout - include some text on the club announcements page that says "Club announcements is a new Ion feature that enables clubs to better communicate with their members. It is currently in beta release and is only available to select clubs. If your club is interested in participating in the rollout, contact [email protected]. The feature will be released to the entire TJ community in the near future."

[JasonGrace2282]

Also add tests along the way :)

[shrysjain]

new: force sponsors to be subscribed to announcements

[JasonGrace2282]

Development has now moved to #1724