due to a bug in clang (https://stackoverflow.com/a/47849501), myMultiTypeBlockvector.size() (which is static constexpr) has to be changed to MultiTypeBlockVector::size() to be used as a constexpr template argument
probably a similar issue with using Dune::Hybrid::forEach and std::get<>
fix several other clang-related errors
fixes #550 (closed)
depends on !1191 (merged)