TaskGroup assignee as quick form.

Binding isn’t quite right. The model isn’t updated/saved when modifying
assignee. But otherwise it works fine. I would also like to get a few
pixels of padding at the top of each task group row. Not sure right now
the best way to do that. Using the PBC Request tree.mustache as a
reference makes me think that the spacing is made correct on that
display by the icons. I’m going to ask for some help on this to get it
done correctly.
Assignee now updates/saves properly.
Merge pull request #1501 from reciprocity/feature/task-group-assignee-quickform

TaskGroup assignee as quick form.