Merge branch 'issue/child_nodes' into 'master'

replace explicit child type deduction with global type-traits

See merge request !264

amdis/localoperators/StokesOperator.hpp

@@ -39,9 +39,10 @@ namespace AMDiS
       static_assert(static_size_v<typename LocalFct::Range> == 1,
         "Viscosity must be of scalar type.");
 
-      using VelocityNode = typename Node::template Child<0>::type;
-      using VelocityCompNode = typename VelocityNode::template Child<0>::type;
-      using PressureNode = typename Node::template Child<1>::type;
+      using VelocityNode = Dune::TypeTree::Child<Node,0>;
+      using VelocityCompNode = Dune::TypeTree::Child<Node,0,0>;
+      using PressureNode = Dune::TypeTree::Child<Node,1>;
+
       static_assert(VelocityNode::isPower && PressureNode::isLeaf, "");
 
       using namespace Dune::Indices;