Check for OMEMO key updates before sending a message
Description of the new feature
Gajim should check on different points in the process of starting a conversation, check if there are key updates with said contact pending. At the moment Gajim trusts the already approved keys. But if a contact has updated their keys the notice that something changed comes after sending the first message. This is quite annoying as one has to resend the message if the key should be included. The window should open before sending takes place.