Remove phpass and migrate to new Hasher interface

This PR removes phpass and migrates to the new Hasher interface.

Please notice that due to https://github.com/owncloud/core/issues/10671 old hashes are not updated but the hashes are backwards compatible so this shouldn't hurt.
Once the sharing classes have a possibility to update the passwords of single shares those methods should be used within the newHash if block.
Merge pull request #12226 from owncloud/remove-phpass

Remove phpass and migrate to new Hasher interface