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