Replace staticForLoop

This replaces staticForLoop with Dune::Hybrid::forEach. Because there is no hybrid replacement for staticFindInRange, the corresponding header needs to stay, though.

I've used std::get<std::decay_t<decltype(i)>::value> instead of std::get<i.value> in quite a few places in compositebasis.hh. It should be noted that the compile errors that clang 3.8 finds for the latter are not found if the corresponding code is only parsed but not instantiated. Since the compositebasistest tests hardly anything that makes up the functionality of the CompositeBasis, this problem only manifests in initializeIndices() and I've silently assumed it to occur in all the other loops, too.