Feature/cleanup std utility

This merge request cleans up the implementation of C++14 integer sequences and also removes an old alias of std::declval() in our Dune::Std namespace.

Warning: After merging this merge request, any use of Std::declval() will cause compilation failures.

looks good. The only question is ... should we immediately drop Std::declval, or keep for compatibility reasons.

Can we merge and close?

As there were no further, objections, I'll go ahead and merge this

Status changed to merged

mentioned in commit 75279b42

Mentioned in commit 75279b42