leads to exception
behaviout shold be:
if a system model )not work item) is droped on a ork package:
if there are leafopeners, which are not closed, put them into the work package.
if there are no leaf openers which are not closed, create aa new action item annotated to the system model lement and ad it to the workpackage. behaviour shall be consistent in the sattsuview on flat and hierachy tab.
generalize this behaviour in taskutil