Index "Closed" and "Unowned" relationships explicitly

Summary: Ref T4365. Two diffs from now, I'm changing the UI a bit to let you search for closed and unowned documents more explcitly. To support this in ElasticSearch and more easily in MySQL search, make these explicit, positive relationships.

Test Plan: `bin/search index --all`

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4365

Differential Revision: https://secure.phabricator.com/D8122