This seems to introduce a new child-less XML element with only attributes
and no content. These are a common XML anti-pattern I think we probably
shouldn't encourage more of.
Two alternatives:
<never xmlns='urn:xmpp:notification-settings:0' />
<notify xmlns='urn:xmpp:notification-settings:0'>never</notify>
Seperate from this concern, in my client I have a fourth possible
notification setting "on reply", which I think it would be useful to
represent.