Update the related user selector to use the new avatars API

Review Request #8985 — Created June 2, 2017 and submitted — Latest diff uploaded


Review Board


The related user selector was previously relying on the
integration_gravatars setting and the deprecated avatar_url field
from the UserResource. The selector now fetches avatar URLs from the
avatar services instead of always using Gravatars.

Tested the related user selector on the repository page with custom
avatars and gravatars. It worked as expected.