Add modification to NewtonMethod to solve nonlinear periodic or hanging-node problems

Currently, there is no functionality to solve nonlinear periodic/hanging-node problems, like StationaryLinearProblemSolver._hanging_node_modifications for linear problems. As far as I can tell, it should suffice to include something like

if (_hanging_node_modifications) {
          auto dirichletValues = solution;
          // keep only Dirichlet values
          Dune::PDELab::set_shifted_dofs(_gridOperator.localAssembler().trialConstraints(),0.0, dirichletValues);
          // set all constrained Dofs to zero in solution
          Dune::PDELab::set_constrained_dofs(_gridOperator.localAssembler().trialConstraints(), 0.0, solution);
          // copy correct Dirichlet values back into solution vector
          Dune::PDELab::copy_constrained_dofs(_gridOperator.localAssembler().trialConstraints(), dirichletValues, solution);
          // interpolate periodic constraints / hanging nodes
          _gridOperator.localAssembler().backtransform(solution);
        }

at the start of the prepareStep() and updateDefect() methods of the NewtonMethod, so that the constrained Dofs are updated accordingly in each Newton iteration, while preserving the correct Dirichlet values.