Diffusion - tag queries => conduit

Summary: title. Ref T2784.

Test Plan: foreach of SVN, Mercurial, and Git, loaded up a repository. Verified that only git had a tags box and it showed up correctly. Went to CALLSIGN/tags and verified that only git had a tags box and it showed up correctly. Went to various commits across vcs and verified it said "none" unless it was a git commit that also was tagged.

Reviewers: epriestley

Reviewed By: epriestley

CC: chad, aran, Korvin

Maniphest Tasks: T2784

Differential Revision: https://secure.phabricator.com/D5894