Clear session before setup

Fixes https://github.com/owncloud/core/issues/11861
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
Merge pull request #11947 from owncloud/public-hash-api

Add OCP\Security\IHasher
Move CSRF check

Because we're closing the session now before controllers are executed there are cases where we cannot write the session.

Conflicts:
	lib/private/server.php