Update _config.php

Moving extension to config.yml for 3.1 compatibility
Update display_logic.yml
Merge pull request #2 from MattyBalaam/patch-1

Update _config.php
Merge pull request #1 from MattyBalaam/patch-2

Update display_logic.yml
Merge pull request #8 from MattyBalaam/master

Move Object::add_extension to config.yml