Add option to enable PGP opportunistically
Currently, if a contact is assigned a GPG key, Gajim encrypts messages, whether the recipient's client is able to decode those messages at this time or not. It would be nice to have an option to allow for "opportunistic" encryption, i.e. encrypt when the recipient is able to receive encrypted, but send unencrypted otherwise and warn the user.
Associate an OpenPGP key with a recipient, then send a message. If the recipient is not using a client that possesses the OpenPGP key, then he/she is unable to decrypt the message. This is NOT a problem, per se, and is probably the way things should work. But having an option to send unencrypted by default in this scenario would be useful.
Please consider adding an "opportunistic" mode to the encryption part.