BUG: Fixed segment visibility indicator bug in subject hierarchy

When a segment was shown/hidden from somewhere else than SH, then the visibility icon in SH was not updated. By emitting modified event on the shown/hidden segment's SH item, the update is triggered.

Also, minor issues were fixed in SHNode::GetDisplayVisibilityForBranch. The new implementation of GetDataNodesInBranch includes the given node's data node itself in the returned collection, so no need to add that explicitly. Also, the exception about segmentation nodes were removed, as it was a workaround in the past when segmentation node was not registered in the scene. Further, the warning about partial visibility for leaf nodes was removed, because it can happen if a data node has more than one display node (e.g. annotations, fiber bundles)

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25864 3bd1e089-480b-0410-8dfb-8563597acbee