Make Drydock more broadly aware of policies

Summary:
Ref T2015. Moves a bunch of raw object loads into modern policy-aware queries.

Also straightens out the Log and Lease policies a little bit: there are legitimate states where these objects are not attached to a resource (particularly, while a lease is being acquired). Handle these more gracefully.

Test Plan: Lint / browsed stuff.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2015

Differential Revision: https://secure.phabricator.com/D7836