Form now updates properly when keys change.

-- When I started copying key nodes instead of assigning references
(when I added validation), I caused a problem where the form wouldn't
update when you modified a key outside of the form.
-- This also affected inserting keys, which would insert keys in a
seemingly random place.
-- I'm now properly updating $scope.multi when I modify properties on
the selected keys.
-- I also deleted the findKeyAfter() function (used only in addKeys),
and using the more-robust sortKeys() method.