Add support for OTP (SB-1055)
Add support for OTP (like Yubikey) on webmail login page. From what I see, it needs : - a new field on the login page to enter the OTP - a new field in the user database to store the Yubikey Key & ID - (possibly) a field on the administration page to set an external validation server. Almost everything is available from https://github.com/Yubico