tried to create flexible ViewPane, 1) SplitPane 2) FlowPane.
but it didn't work because 1) is a Control, 2) is a Pane/Region
removed static from the nested classes just introduced and renamed them
changed return type of viewNode to Parent, common ancestor of 
SplitPane, FlowPane, etc
changed name to StructureViewContainer
changed nested class names again by removing "Structure"
renamed viewNode() to asNode();
placed code to create the viewContainer into their own methods;
all compile errors fixed