Diffusion - move DiffusionBrowseQuery => Conduit

Summary: see title. Ref T2784.

Test Plan:
In diffusion, for each of SVN, Mercurial, and Git, I loaded up /diffusion/CALLSIGN/. I verified the README was displayed and things looked good. Next I clicked on "browse" on the top-most commit and verified things looked correct. Also clicked through to a file for a good measure and things looked good.
In owners, for each of SVN, Mercurial, and Git, I played around with the path typeahead / validator. It worked correctly!

Reviewers: epriestley

Reviewed By: epriestley

CC: chad, aran, Korvin

Maniphest Tasks: T2784

Differential Revision: https://secure.phabricator.com/D5883