The material balance scaling is extended to the solvent model
The gas value is used as default and an updateEquationsScaling() method
is added.
Minor modifications is done to the BlackoilModelBase.hpp and
BlackoilModelBase_impl.hpp in order to re-use code from the base case.
Solvent is accounted for in the calculations of well connection
pressures by adjusting the surface_density and the b-factor
TODO: Restructuring to avoid code duplication with
BlackoilModelBase_impl
