Isosurface Labeling and Persistence Based Simplification

The changes in this branch relate to contour tree simplification and isosurface extraction. Over the summer I worked with Gunther Weber and Oliver Ruebel at the Lawrence Berkeley National Laboratory and this is my contribution to the project.

There are two new features in this branch - isosurface connected component labeling and contour tree persistence based simplification.

The first new features is isosurface component labeling. This features labels the triangles an isosurface extracted via marching cubes based on which superarc in the contour tree they belong to.

The second feature is a new parallel persistence based simplification method. It works similarly to the current volume based simplification, but it uses the persistence of a branch as a guiding metric.