Merge branch 'feature/improve-staggered-vtk' into 'feature/iofields'

Feature/improve staggered vtk

See merge request !1256 (merged)

(cherry picked from commit b5d6b124)

5f8517b3 [navierstokes][iofields] Use two separate function for cell and face dofs a372c386 [test][io][staggeredvtknames] Delete output files