Replacing PHPass with password_compat

Per https://github.com/owncloud/core/issues/10050#issuecomment-51333177

also https://github.com/owncloud/3rdparty/pull/110
Yes. We need to:

1. Deprecate the passwordsalt officially for ownCloud 8 and then remove it for ownCloud 9
2. Migrate all places that used the password salt for encrypting stuff to the new security utils