Add Filters/GeometryPreview module

The Filters/GeometryPreview module has been added which includes filters for creating a preview of the geometry of a dataset. As of now, it includes the vtkPointSetToOctreeImageFilter and vtkOctreeImageToPointSetFilter filters.

1. vtkPointSetToOctreeImageFilter can be used to convert a point set to an image with a number of points per cell target and an unsigned char octree cell array. Each bit of the unsigned char indicates if the point-set had a point close to one of the 8 corners of the cell. It can optionally also output a cell array based on an input point array. This array will have 1 or many components that represent different functions i.e. last value, min, max, count, sum, mean.
2. vtkOctreeImageToPointSetFilter can be used to convert an image with an unsigned char octree cell array to a point set. Each bit of the unsigned char indicates if the cell had a point close to one of its 8 corners. It can optionally also output a point array based on an input cell array. This array will have 1 of the components of the input array.