Adjust to the in-house style

- Use jbuilder instead of hashes
- Use resource instead of direct HTTP verbs
    Verbs only make sense if you have one or two routes, if there are
    multiple that emulate what resource does then it's better to use resource.
- Paginate using link headers
- Cache responses

app/views/users/_user.json.jbuilder

@@ -0,0 +1,5 @@
+json.cache! user do
+  json.(user, :id, :name, :role)
+
+  json.avatar_url fresh_user_avatar_url(user)
+end