Update DC_General.php

Fixed check for changes of the widget value
Add support for adding/removing buttons
Update sorting - Use the field sorting flag if exists, instead of the global sorting flag.
Add support for adding/removing buttons
Adding composer.json
Bugfix: make ajax calls work again after commit a8b6c826f61cc1640c92a091e050dae6c5a5dc71.
We MUST NOT reload automatically submitted post requests.
Bugfix wrong if statement in the panel template