Distinguish between "Remote URI" and "Clone URI" in Repositories

Summary:
Hosted repositories have muddied this distinction somewhat. In some cases, we only want to use the real remote URI, and the call is only relevant for imported repositories.

In other cases, we want the URI we'd plug into `git clone`.

Move this logic into `PhabricatorRepository` and make the distinction more clear.

Test Plan: Viewed SVN, Git, and Mercurial hosted and remote repositories, all the URIs looked reasonable.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran, dctrwatson

Differential Revision: https://secure.phabricator.com/D8096