Fixed destroy element bug which may lead to segmentation fault. Now child selection group is responsible for notifying the parent group when it is destroyed. Tracker item 2668, https://tracker.physiomeproject.org/show_bug.cgi?id=2668
Fixed destroy element bug which may lead to segmentation fault. Now child selection group is responsible for notifying the parent group when it is destroyed. Tracker item 2668, https://tracker.physiomeproject.org/show_bug.cgi?id=2668

git-svn-id: 4705079bc6b8aadf675e3696f5c015a6aa4916e3@8003 3c1deb5b-d424-0410-962d-aba41a686d42

hsorby/zinc,OpenCMISS/zinc,hsorby/zinc,OpenCMISS/zinc,hsorby/zinc,OpenCMISS/zinc,hsorby/zinc,OpenCMISS/zinc