Return a pointer to the material manager

This is used by blackoilintensivequantities.hh. Further, for other
problems derived from MultiPhaseBaseProblem, that base class will
return a null pointer such that problems that do not override the
materialLawManagerPtr() method still can use the blackoil intensive
quantitites (which in the case of directional relative permeabilities
makes use of the problem reference to access the materialLawManager)

ebos/eclproblem.hh

@@ -1505,6 +1505,12 @@ public:
     std::shared_ptr<const EclMaterialLawManager> materialLawManager() const
     { return materialLawManager_; }
 
+    // TODO: See discussion in multiphasebaseproblem.hh for the reason why we need this method
+    const EclMaterialLawManager* materialLawManagerPtr() const
+    {
+        return materialLawManager_.get();
+    }
+
     /*!
      * \copydoc materialLawManager()
      */