This reverts commit 0df070a8.

Limit the size of the string generating the preview image for TXT files

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

Despite the documentation this function does not read values from the cookie

We do not want to redirect to other domains using the "?redirect_url=" feature. Please notice, that the ownCloud project does not consider open redirectors as security issue.

for group shares only the parent has the up-to-date permission. Make sure that we always use this permission, except if the user permission is '0' because in this case the user unshared the group share from self

call \OCP\Share::getItemsSharedWithUser() to get exclude list, this way all checks are executed, e.g. to check if the share is really visible

a

calendar or contacts app. It doesn't make sense to build a exclude list by the
share API, the apps knows best which are valid targets.