better workspace_menber schema

tracim/tests/functional/test_workspaces.py

         assert user_role['role'] == 'workspace-manager'
         assert user_role['user_id'] == 1
         assert user_role['workspace_id'] == 1
+        assert user_role['workspace']['workspace_id'] == 1
+        assert user_role['workspace']['label'] == 'Business'
+        assert user_role['workspace']['slug'] == 'business'
         assert user_role['user']['public_name'] == 'Global manager'
+        assert user_role['user']['user_id'] == 1
         # TODO - G.M - 24-05-2018 - [Avatar] Replace
         # by correct value when avatar feature will be enabled
         assert user_role['user']['avatar_url'] is None

tracim/views/core_api/schemas.py

     user_id = marshmallow.fields.Int(example=3)
     workspace_id = marshmallow.fields.Int(example=4)
     user = marshmallow.fields.Nested(
-        UserSchema(only=('public_name', 'avatar_url'))
+        UserDigestSchema()
+    )
+    workspace = marshmallow.fields.Nested(
+        WorkspaceDigestSchema(exclude=('sidebar_entries',))
     )
 
     class Meta: