Clear session before setup

Fixes https://github.com/owncloud/core/issues/11861
Remove confusingly names \OC\User\Manager::delete and fix the automatic cache cleanup instead
Merge pull request #11972 from owncloud/usermanager-remove-delete

Remove confusingly names \OC\User\Manager::delete and fix the automatic ...
Merge pull request #11883 from owncloud/clear-session-for-setup

Clear session before setup
update to 3rdparty master
Add OCP\Security\IHasher

Public interface for hashing which also works with legacy ownCloud hashes and supports updating the legacy hash via a passed reference.

Follow-up of https://github.com/owncloud/core/pull/10219#issuecomment-61624662
Requires https://github.com/owncloud/3rdparty/pull/136