Merge UFEM related changes

Overview of the changes:
* Segregated semi-implicit solution for incompressible Navier-Stokes
* Periodic mesh partitioning and LSS support
* LSS vector operations (update, apply matrix, ...)
* CGAL point cloud tetrahedralizer (was failed attempt at getting a mesh tetrahedralizer)
* VTK plugin which for now only does tetrahedralization