add flow_ebos, an ebos based simulator

it uses ebos for linearization of the mass balance equations and the
current flow code from opm-simulators for all the rest. currently, the
results match the ones from plain `flow` for SPE1, SPE9 and Norne, but
performance is not optimal: on SPE9, converting from and to the legacy
data structures takes about a third of the time to do the actual mass
balance assembly. nevertheless `flow_ebos` is almost as fast as plain
`flow` for SPE9. (for Norne `flow_ebos` is about 15% slower, even
though the results match quite closely. the reason for this is that it
requires more iterations for some reason.)

opm/autodiff/NonlinearSolver_impl.hpp

@@ -110,7 +110,6 @@ namespace Opm
     }
 
 
-
     template <class PhysicalModel>
     int
     NonlinearSolver<PhysicalModel>::
@@ -169,7 +168,6 @@ namespace Opm
     }
 
 
-
     template <class PhysicalModel>
     void NonlinearSolver<PhysicalModel>::SolverParameters::
     reset()