Update Makefile to generate meshes for Navier-Stokes

Generate series of meshes roughly doubling in size. Prevent the .msh
files from being deleted as intermediates.
Convert Navier-Stokes benchmarks to pybench
Add optional norm computation to Navier-Stokes benchmark
Enable mesh reordering for DOLFIN Navier-Stokes benchmark
Use block jacobi PC with ilu inner PC for Navier-Stokes
Script data collection and plots for Navier-Stokes
Convert Cahn-Hilliard benchmarks to pybench