delete all children's previews when deleting a folder

add phpdoc
Testcase base class
Do not use uniqid in Group and User tests as it is not unique on windows
Test LargeFileHelperGetFileSize also with ascii only characters

And skip the UTF8 names on Windows as they are not supported
Windows does not support CHMOD, therefor we can not test not writable folders
Add \OC\App\Manager to handle enabling/disabling apps
eliminate OC_Template::printErrorPage in database classes, fixes #12182
Refactor file sharing public link handling

fixes download issue introduced by #10755

Conflicts:
	apps/files_sharing/public.php
Added download size on public sharing
Show warning when invalid user was passed

Sometimes there are bugs that cause setupFS() to be called for
non-existing users. Instead of failing hard and breaking the instance,
this fix simply logs a warning.
errors are already logged
do not output DB information, and do not set header
Merge pull request #11029 from owncloud/fix-share-download

Fix share download
[tx-robot] updated from transifex
Check if app is enabled for user

Fixes https://github.com/owncloud/core/issues/12188 for AppFramework apps
Merge pull request #12189 from owncloud/checkIfAppIsEnabled

Check if app is enabled for user
Merge pull request #12186 from owncloud/fix-12182

eliminate OC_Template::printErrorPage in database classes, fixes #12182
[tx-robot] updated from transifex
[tx-robot] updated from transifex
Skip some more tests on Windows which just can not work at all