Support multiple LDAP filters in the Phabricator UI

Summary: Ref T3208. Not ready for prime time yet.

Test Plan: ldap T.T

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley, frgtn, aran

Maniphest Tasks: T3208

Differential Revision: https://secure.phabricator.com/D8160