[C++11] Remove a leftover SelectType and replace it with conditional
[Geometry] Remove the StoreGeometryReference specializations for our geometries

Those specializations are not needed anymore after the release of Dune 2.3.
[MultiDomainGrid] Work around restrictive implementation type access

The conversion method from host IntersectionIterator to the
MultiDomainGrid version fails because the typedef for the iterator
implementation cannot be accessed anymore without setting the stupid
experimental grid features flag. However, Grid::getRealImplementation()
still works... >:)

So this patch does some ugly magic with decltype to get at the required
type. Take that, restrictive access policy!
[SubDomainGrid] Fix some bitrot in the subDomainIntersectionIterator() methods
[Traits] Add new constexpr static function to query whether the maximum subdomain number is a compile-time constant
[MultiDomainGrid] Provide access to the stored instance of the MDGridTraits
[MultiDomainGrid] Some template magic to exploit a statically known maximum subdomain number

The maximum subdomain number can only be retrieved using a function,
because there are now some traits versions that allow setting this
number at runtime.
On the other hand, it would be nice to still have it available as a
compile-time constant if possible.
This patch does exactly that by making the method static constexpr if
the number is known at compile time, and a regular const member function
otherwise.
[MultiDomainMCMGMapper] Make compatible with new maximum subdomain index querying and dynamic values for the maximum

The patch works by using a std::array if the number is known at compile
time and a std::vector otherwise. In order to correctly handle the
different initialization requirements (the vector needs to allocate
dynamic memory of the right size), the actual storage has been moved to
a mixin base class that contains the variables and handles the
initialization in its constructor and that is specialized for the
different storage schemes.
[testlargedomainnumbers] Test dynamic maximum subdomain index values as well as static ones
Replace more SelectType and GenericReference* occurrences

Edited by Steffen to remove the SelectType change already in the local tree.
Cleanup tests

Use Yasp constructor from Dune 2.3.
Do not include deprecated/removed gfgridtype.hh.
Replace tabs by spaces.
Adjust absolute dune-grid-howto paths to relative ones.