Update cryptlib to 3.4.7

TLS 1.3 is still not usable due to Cryptlib not supporting HelloRetryRequest.

SSH public key authentication support added. Use OpenSSH authorized_keys format in data/user/%04d.sshkeys. There's currently no way for a user to edit this file, but it's planned to do this using sftp.

TLS 1.0 and 1.1 are now disabled. Refer to RFC-8996 for the reasons.

Multiple SSH channels are now usable.

SyncTERM will now attempt to append the current public key to .ssh/authorized_keys using sftp on connecting. This can be disabled with a new per-BBS setting.