Add Admin interface

[Matt Lindsey]

Add a special 'admin' interface that would allow authorized people to do maintenance on the app. For example deactivate/delete spam users and/or projects, load the static pages, 'pin' important projects to the top of the Projects page.

Here is a potential framework to utilize: https://github.com/activeadmin/activeadmin

Or this is newer and uses rails 7 features (I think): https://github.com/avo-hq/avo

Add any ideas to this Issue, then we can discuss what to do, and potentially create multiple Issues and/or PRs.

[Matt Lindsey]

We probably want to hold off on this one, since the E-Learning project plans to add the rolify and pundit gems (rather than Avo), which would handle this functionality.