Make TopoShape::_Shape a private member variable

[ezzieyguywuf]

I have submitted a pull request to make TopoShape::_Shape a private member variable with access methods TopoShape::getShape() and TopoShape::setShape(). This is intended as the first step towards a Topological Naming solution. Don't get too excited b/c other Topo Naming pull requests are still a ways down the road, but as I had completed this work on my local branch I felt it would not hurt to go ahead and merge it into upstream.