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

This reverts commit 09fd34ee.

This adds a file lock to the config in hope that this prevents race conditions as reported in https://github.com/owncloud/core/issues/11070

Testplan:

- [ ] Delete config.php and make it read-only => Error is thrown that it is not writeable
- [ ] Installation still works
- [ ] Changing config settings works (i.e. using the SMTP config switches in the administration menu)
- [ ] Your PC didn't blow up
- [ ] Installing the news app and the "Disable AppCode checker" app did not destroy your installation

Only skip the main config

Otherwise read only additional configs might not be processed

Test on tmpdir

make search non-static, add ISearch to server container, make legacy a static wrapper for it, move provider and result to public api

This fixes errors where apps would try to start providers using
OC_Search and would fail. Also, made OC_Search simply inherit from
\OC\Search.

* test case added to avoid adding them later

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

And is when using index.php as entry point

Conflicts:
	lib/private/vcategories.php