adapt to new [general] directory in cfg file

dune/tectonic/factories/twoblocksfactory.cc

@@ -76,10 +76,10 @@ void TwoBlocksFactory<HostGridType, VectorTEMPLATE>::setBodies() {
         std::cout << "Grid" << i << " max diameter: " << maxDiameter << std::endl;
     }
 
-    bodyData_[0] = std::make_shared<MyBodyData<dim>>(this->parset_.sub("body0"), this->parset_.template get<double>("gravity"), zenith_());
+    bodyData_[0] = std::make_shared<MyBodyData<dim>>(this->parset_.sub("body0"), this->parset_.template get<double>("general.gravity"), zenith_());
     this->bodies_[0] = std::make_shared<typename Base::LeafBody>(bodyData_[0], grids[0]);
 
-    bodyData_[1] = std::make_shared<MyBodyData<dim>>(this->parset_.sub("body1"), this->parset_.template get<double>("gravity"), zenith_());
+    bodyData_[1] = std::make_shared<MyBodyData<dim>>(this->parset_.sub("body1"), this->parset_.template get<double>("general.gravity"), zenith_());
     this->bodies_[1] = std::make_shared<typename Base::LeafBody>(bodyData_[1], grids[1]);
 }