Send subscription request to gateway (outside normal registration flow)

When my gateway (cheogram.com) sends a <presence type="subscribe" /> to Gajim, it gets back a <presence type="subscribed"/>. But Gajim never sends (nor asks the user about sending) a <presence type="subscribe" /> to the gateway.

This is an unsolicited (from PoV of Gajim) subscription that is caused by a web interface. Removing roster item and re-adding it causes subscription to work as expected. Would be fine to ask user "do you want to subscribe?" as Gajim would do with any other subscription request. In fact, currently Gajim auto-approves the subscription request, which is also a potential privacy leak (anyone could claim to be a gateway and get user presence that way). Non-registration-flow presence subscriptions from JIDs claiming to be a gateway should be handled in the same way (and by the same code) as from any other JID.