R1:1e42c62b8f5c

Make ManiphestTaskQuery a (mostly) policy-aware query

Summary: Ref T603.

Test Plan: Viewed home and maniphest, fiddled all the knobs.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D6930