Made _join more powerful and easier to use
Fixed the partial-edit bug

Major bug in the wedding site: when I edited an invitee, their RSVP was
getting stomped!

Did this as a fairly conservative change for now.  Need to rethink how
these messages work in the near term.
Lists of Links in the Editor are now sorted

By displayName, which seems obvious
Tightened up the display of email recipients
Provided a better front display for Spaces

Took the experiments I've been working up for displaying the Thing Tree,
and reified it into a couple of system objects.

System Space displays this way by default.  Changed things so that new
Spaces inherit from System, so they will also display this way.