Add support for Woltlab Burning Board 4.x hashes

[kholia]

See https://github.com/WoltLab/WCF/blob/master/wcfsetup/install/files/lib/util/PasswordUtil.class.php for details.

The new algorithm is "double salted bcrypt hash".

[marksilinio]

actual link:
https://github.com/WoltLab/WCF/blob/master/wcfsetup/install/files/lib/system/user/authentication/password/algorithm/DoubleBcrypt.class.php