Star delegate example

The Star Delegate example shows how to create a delegate that can paint itself 
and that supports editing.

I did change the behavior a minor bit, since it feels silly to be forced to
select _and_ double click an item in order to trigger editing. Double clicking
should suffice, no matter if a row is selected or not, doesn't it? Also these
stars get activated, if the pointer crosses its center horizontally. Hence, a
zero star voting is possible, too.

Hans-Peter Jansen
