Merge pull request #248 from barche/master

Merge UFEM related 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
[ENH] UFEM: Test partitioning on periodic channel
[FIX] BlockData 2D surface orientation
[FIX] More robust periodic partitioning