Per-client SASL certificates

[3nprob]

This enables CertFP authentication for both users and bots. #1062 reuses the same certificate across all users. In order to make the isolation here clear, bot certificates are read from botConfig. Users can manage their own certs and keys in a similar fashion to passwords.

Adds bot commands: storekey, removekey, storecert, removecert.

:warning: Depends on #1462 (or other fix to allow encrypting longer inputs) to work properly