adding the member variables to MultisegmentWells

and ther public interfaces. Probably the mutable interfaces can be
removed after moving the functions to the Wells class.

opm/autodiff/BlackoilMultiSegmentModel_impl.hpp

@@ -95,7 +95,7 @@ namespace Opm {
         , segment_comp_surf_volume_current_(fluid.numPhases(), ADB::null())
         , segment_mass_flow_rates_(ADB::null())
         , segment_viscosities_(ADB::null())
-        , ms_wells_(wells_multisegment)
+        , ms_wells_(wells_multisegment, fluid.numPhases())
     {
     }