Update User screens

* Add `modified` field to user endpoints. The API returns the last login
date as the `modified` field to the users.
* Add modified to user details.
* Modify user form layout to be as per mockups.
* Remove `last name` and  `first name` from user row, since it is
already on the column title.

closes: https://github.com/ansible/awx/issues/5687
closes: https://github.com/ansible/awx/issues/9564

awx/api/serializers.py

@@ -948,7 +948,6 @@ class UserSerializer(BaseSerializer):
             '*',
             '-name',
             '-description',
-            '-modified',
             'username',
             'first_name',
             'last_name',