Add support for the SSH "none" auth method.

This is used by some BBSs to enable encryption without needing to
integrate the BBS user base into their SSH server (and presumably
so they don't need to run multiple SSH servers).  All users log in
with the same username (ie: "bbs") and no password is requested or
required.

Once the BBS starts, it prompts for the BBS user name and password
as normal.

In SyncTERM, the user/password/syspass fields are redefined as
SSHuser/BBSuser/BBSpassword and they are moved around when you
change the connection type.  This means that if you change a listing
that has a syspass to SSH (no auth) and back, the syspass is lost.

I'm not sure if I plan to fix this or not.