R1:60f7534e3ed7

Add a "Diviner" application with documentation links

Summary:
See D3572.

- Make "Diviner" show up on `/applications/`.
- Give it a landing page with links to documentation.

I have a parital port of Diviner proper into Phabricator in a branch, but it's a big chunk of work away from being landable.

Test Plan: Viewed `/applications/`, saw Diviner, clicked it, got documentation links.

Reviewers: vrana, btrahan

Reviewed By: vrana

CC: aran

Differential Revision: https://secure.phabricator.com/D3580