This adds the integration tests for the CSRF protection on the DAV backend introduced with 9.0.

Fixes https://github.com/owncloud/core/issues/22598

* user with a quota of 0 gets a file shared and can't update this file
  because the wrong quota is used to verify if the update is allowed

Recent refactorings have resulted in the header being added twice, this makes browsers ignore the header which removes any security gains.

This changeset adds the header only once and adds integration tests ensuring the correct header in future.

https://github.com/owncloud/core/issues/22577

This adds integration tests for the comments. Especially with regard to the permission handling, didn't find any problem in it.

Fixes https://github.com/owncloud/core/issues/22367

Moves the update notification code in a single app. This is required since we want to use SSO for the new updater and for this have some code running in ownCloud as well (and we don't want that in core neccessarily). This app can provide that in the future, right now it's only the update notification itself. Will continue working on the SSO right away but wanted to keep the PR small.

Furthermore also makes some more code unit-testable...

The new sharing code handles things differently so there is no way for
create shares to handle this all properly.

Else we run into race conditions with the skeleton code

This commit consists of patches automatically generated for this project on https://scrutinizer-ci.com

* Small changes plus check of the file using propfind
* Restaured line removed accidentally