CGAL mesh simplification procedures

Look for replacement of remesher with the more widely used and test [CGAL](http://www.cgal.org/index.html) library, while trying to keep track of the region mapping directly (#46) (which assumes avoiding complete remeshing of the surface as we are doing now)

Maybe using [this](http://doc.cgal.org/latest/Surface_mesher/index.html#Chapter_3D_Surface_Mesh_Generation), however I believe this is what is used in [iso2mesh](http://iso2mesh.sourceforge.net/cgi-bin/index.cgi/), which was not good too keep the depth of the sulci while downsampling the surface.