added 'using namespace' inside generic lambdas to workaround an intel compiler bug

Related to issue #31 (closed)

More changes of the form

ifElse(condition, [&](auto&& id) {
  using namespace Dune::Hybrid; // needed for icc, see issue #31
  forEach(range, [&](auto&& entry) { ... });
});

where necessary. The errors occurred after fixing some other issues.