Fix tests/test_blockmesh.py

I realize that there are some functions defined in tests/test_blockmesh.py (create_code_phill, create_code_phill_3d_extrusion) which are not executed at all.

I guess these functions have to be moved into doc/examples/fluidsimfoam-phill/src/fluidsimfoam_phill/blockmesh.py and that some tests have to be written to execute them.