Unban releeph product name "branch"

Summary:
Fixes T3657. We no longer construct ambiguous URIs, so product names are no longer restricted.

Also fix some minor URI construction stuff.

Test Plan: Created a product called "branch".

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T3657

Differential Revision: https://secure.phabricator.com/D8767