Various Navier-Stokes solvers implemented in FEniCS.

Structure of solver-problem as well as some problems and solvers are borrowed
from the existing FEniCS Navier-Stokes solvers, namely

 nsbench    https://code.launchpad.net/~nsbench/nsbench/main 
 cbcflow    https://bitbucket.org/simula_cbc/cbcflow 
 Oasis      https://github.com/mikaem/Oasis