rename display_name as public_name in endpoint

tracim/models/context_models.py

         return self.user.user_id
 
     @property
+    def public_name(self) -> str:
+        return self.display_name
+
+    @property
     def display_name(self) -> str:
         return self.user.display_name
 

tracim/tests/functional/test_session.py

             params=params,
             status=200,
         )
-        assert res.json_body['display_name'] == 'Global manager'
+        assert res.json_body['public_name'] == 'Global manager'
         assert res.json_body['email'] == 'admin@admin.admin'
         assert res.json_body['created']
         assert res.json_body['is_active']
             )
         )
         res = self.testapp.get('/api/v2/sessions/whoami', status=200)
-        assert res.json_body['display_name'] == 'Global manager'
+        assert res.json_body['public_name'] == 'Global manager'
         assert res.json_body['email'] == 'admin@admin.admin'
         assert res.json_body['created']
         assert res.json_body['is_active']

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['user']['display_name'] == 'Global manager'
+        assert user_role['user']['public_name'] == 'Global manager'
         # 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

         required=True,
         example='suri.cate@algoo.fr'
     )
-    display_name = marshmallow.fields.String(
+    public_name = marshmallow.fields.String(
         example='Suri Cate',
     )
     created = marshmallow.fields.DateTime(
     user_id = marshmallow.fields.Int(example=3)
     workspace_id = marshmallow.fields.Int(example=4)
     user = marshmallow.fields.Nested(
-        UserSchema(only=('display_name', 'avatar_url'))
+        UserSchema(only=('public_name', 'avatar_url'))
     )
 
     class Meta: