[PL] Add initialize to local assemblers.

Some of the local assembler initialization cannot
be done in its constructor but after initial conditions
have been set. This function allows such initialization
procedures.

ProcessLib/LocalAssemblerInterface.cpp

@@ -91,6 +91,13 @@ void LocalAssemblerInterface::setInitialConditions(
     setInitialConditionsConcrete(local_x, t);
 }
 
+void LocalAssemblerInterface::initialize(
+    std::size_t const /*mesh_item_id*/,
+    NumLib::LocalToGlobalIndexMap const& /*dof_table*/)
+{
+    initializeConcrete();
+}
+
 void LocalAssemblerInterface::preTimestep(
     std::size_t const mesh_item_id,
     NumLib::LocalToGlobalIndexMap const& dof_table, GlobalVector const& x,

ProcessLib/LocalAssemblerInterface.h

@@ -39,6 +39,9 @@ public:
         NumLib::LocalToGlobalIndexMap const& dof_table, GlobalVector const& x,
         double const t);
 
+    virtual void initialize(std::size_t const mesh_item_id,
+                            NumLib::LocalToGlobalIndexMap const& dof_table);
+
     virtual void preAssemble(double const /*t*/,
                              std::vector<double> const& /*local_x*/){};
 
@@ -116,6 +119,8 @@ private:
     {
     }
 
+    virtual void initializeConcrete() {}
+
     virtual void preTimestepConcrete(std::vector<double> const& /*local_x*/,
                                      double const /*t*/, double const /*dt*/)
     {