Directory page should include descriptions of the test pages

[amandabaker]

It'd be great to organize the directory page better so that

1. It's easy to find a test page for whatever I want to test
2. I have a reminder of what each test page does, and which ones are faking out APIs vs which ones use legit APIs

[amandabaker]

Related: Organized the directory page to group apps into: up-to-date/outdated apps, wco/empty/other apps. e86c366