BUG #14299: Fixed missing "modified" notification.

pqScalarValueListPropertyWidget wasn't firing appropriate signal when a range of
values were added to the widget. Fixed that.

Change-Id: I70581a3aacaddcc760290bc5d5b519c20d57de43
Merge topic '14299_fix_contour_panel' into next

bffda43 BUG #14299: Fixed missing "modified" notification.