Allow table sorting on the Relationships page

It would be great to be able to sort the list of relationships by clicking the various table headers. I took a stab at it and got it working OK with some pretty minor changes to the actual module code. However, for some reason, I couldn't get the second table column to sort alphabetically after the first one. Anyway, at least it works on the first column for now.

Totally awesome module, by the way!