Prosody changed its role scheme to only support a single primary role
for each user. In addition, the names of the built-in roles have been
changed. We thus follow those changes to be compatible with the most
recent trunk.
One open question is whether we should switch admin -> operator here,
too (operator being a server-wide admin), but so far there's no need
to.
This aggregates the user actions behind a single "edit" button on
the list view, making it less crammed. It also offers the
functionality of actually editing the user, mind.
Also in preparation for #42.
Requires https://hg.prosody.im/prosody-modules/rev/5bc706c2db8f.
