Notify about certificate fingerprint changes
Please note by far the quickest way to get a new feature is to file a Merge Request.
Description of the new feature
In light oh the MitM attack which is going around XMPP communities over the past few days, I suggest that gajim warns the user when the server fingerprint changes and forcing them to manually acknowledge this change.
Claws mail does this when the server fingerprint changes. I feel this would be a first point at which a MitM attack could be caught, if a certificate is renewed too soon (say if it still has 60 days left on it, it would be pretty unusual to renew it until it hits 30 days).