Make it possible for a Nuxeo user to load the working branch of a given user.

Goal: make it easy to help people when at Support.

As a Nuxeo user I want to be able to load in a sandbox the state of any NOS user working branch.
I can bind a Nuxeo Platform instance to this sandbox so as to test the config of that working branch.
I can save some modifications in the Studio project and update the Nuxeo Platform with it.
For now, I cannot push back any modification to the working branch of that user.