Chat states not send / chat states should use caps
Sometimes it happens that you received a message from a user that supports chat states, but that message was without chat states (for example, it was an offline message). As Gajim now thinks that user doesn't support chat state notifications, it will not send them. This leads to the problem that chat states will never be send - if both users use Gajim, they both need to restart Gajim in order to get chat state notifications working again.
The correct solution would be to look at the caps if chat state notifications are supported. Unfortunately, it seems no client announces support there (not even Gajim). So I'd propose to check for it the current way AND with caps. This means: If we got a message without chat state notifications, BUT the other end announces support for it in caps, we should send chat state notifications. That would solve the problem where 2 Gajim users don't use chat state notifications due to an offline message.