need to be able to retire projects

[willkg]

The Projects list is long, but most of them are not active. We need a way to be able to "retire" projects such that they don't show up in the list.

Things this probably needs:

1. a cli interface or a page on the site that shows projects that haven't seen activity in some period of time
2. a cli interface or a page that lets us retire and unretire projects
3. fix the projects menu to only show active projects
4. a page on the site that lists all the projects, links to them, date of last activity, and whatever other details are interesting

We might even want to nix the Projects drop down and have it instead be a link to the projects page.

This issue covers figuring this out.