Merge branch 'deprecate-alignmentof' into 'master'

Deprecate dune/common/alignment.hh

alignment.hh provides Dune::AlignmentOf<T>::value which is identical to std::alignment_of<T>::value.
This merge request replaces use of AlignmentOf with the shorter alignof() operator introduced in C++11 and deprecates the header.

See merge request !6