This reduces the number of file writes we do for config.php and therefor
hopefully helps lowering the chances for empty config.php files

* keep old static methods - mapped to new ones and deprecated
* removed deleteApp, getUsers, getApps because they are unused
* make AllConfig unit tests more robust against not cleaned up environments

Stop my IDE and Scrutinizer from complaining.

Fixes https://github.com/owncloud/core/issues/10624

Fix copy paste fail

Add unittest for comma separated headers

Revert 3rdparty

This patch was automatically generated as part of the following inspection:
https://scrutinizer-ci.com/g/owncloud/core/inspections/cdfecc4e-a37e-4233-8025-f0d7252a8720

Enabled analysis tools:
 - PHP Analyzer
 - JSHint
 - PHP Copy/Paste Detector
 - PHP PDepend