duplicated code in Stokes+IB FAC operator implementations

[boyceg]

Currently the Box and Level smoothers for the Stokes + IB equations are virtually identical. The code needs to be refactored. It looks like the Box smoother could be supported by the Level smoother.

[amneetb]

I would wait and see how this class pans out for some of the options that we are trying, e.g., cuSPARSE solvers. If it doesn't do any good we would probably wipe out this class from the library as it doesn't do a good job in practice, e.g., in parallel runs.