User schema: the vocabulary ID is displayed instead of the label

 Repro steps: 

To help with the repro, just drop the attached jar into nxserver/plugins and restart Nuxeo. This jar corresponds to the tag "ENV-FOR-WEBUI-592", branch feature/ged-administrative-scp, in my cchampain's Sandbox.

1. In Studio
   1. Create a vocabulary
   2. Create a custom user schema with a field referencing the vocabulary in step 1
2. In a running Nuxeo local instance
   1. Create a new user (and refresh the page)
   2. Edit the user

 
Outcome: 

In the user View, the vocabulary ID is displayed instead of the label.

Expected behavior:

The vocabulary label should be displayed.

Observations / Suggested fix:

We found out that the request header

-H 'fetch-document: properties'

is missing from the GET request headers for

GET http://localhost:8080/nuxeo/api/v1/user/<username>

When this header is added to the GET request, the response contains the correct entity type for the vocabulary field.