[cleanup] Remove check and fallback code for static_assert.

Deprecate header and macro dune_static_assert.
Use static_assert instead.
[cleanup] Remove check and fallback code for initializer list.
[cleanup] Remove check and fallback code for std::conditional.
[cleanup] Remove check and fallback code for std::array.
[cleanup] Remove check/fallback code for std::shared_ptr, std::make_shared.
[cleanup] Replace dune_static_assert by C++11's static_assert.
[cleanup] Remove check/fallback code for variadic templates, SFINAE.
[cleanup] Remove check for rvalue references.
[cleanup] Remove check and fallback code for std::tuple.
Minor fixes related to previous cleanup commits.
Merge branch 'p/gruenich/remove-CXX11-checks'