vtkPolyDataNormals: Split into separate classes

vtkPolyDataNormals used to be a single class that performed, splitting of strips, orienting polygons, splitting sharp edges, and computing normals. This class has been split as follows to make it easier to use and understand.

1. vtkTriangleFilter now has an option to PreservePolys, so that only strips can be split.
2. vtkOrientPolyData is a new class that orients polygons.
3. vtkSplitSharpEdgesPolyData is a new class that splits sharp edges.
4. vtkPolyDataNormals now only computes point and cell normals.

The new classes are more efficient and easier to use and read than the old vtkPolyDataNormals class.

Additionally, vtkAbstractCellLinks now also have ShallowCopy which is used to copy the cell links to avoid copying/rebuilding them.

Moreover, vtkStaticCellLinks's BuildLinks for vtkPolyData has been fixed and multi-threaded.

Finally, vtkPolyData when Editable is Off, vtkStaticCellLinks is used to create the cell links.