The surface density input in well_perforation_densities() in
WellDensitySegmented.hpp is changed from one value pr. phase to one
value pr phase and perforation. This allow for different densities in
different perforation. The test is changed accordingly.
Conflicts:
opm/autodiff/FullyImplicitBlackoilSolver.cpp
To resolve conflicts, WellState was changed to WellStateFullyImplicitBlackoil
in multiple places, and perfRate() changed to perfPhaseRate() in
WellDensitySegmented.