Rough in the new custom URI panel
Summary: Ref T10748. Ref T10366. No support for editing and no impact on the UI, but get some of the basics in place.
Test Plan: {F1223279}
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T10366, T10748
Differential Revision: https://secure.phabricator.com/D15742