BUG: Minor fixes in subject hierarchy

There was a double scrollbar in case of many nodes (one for the module panel, one for the tree view), which was not convenient or nice. The tree view scrollbar has been disabled, so now the same behavior can be seen as in the Data module.
Parse local data plugin fixed so that data nodes do not stay around after creating subject hierarchy from them.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23538 3bd1e089-480b-0410-8dfb-8563597acbee