[localevaluation.swipdg] * use common function for default_beta, inner_sigma and boundary_sigma * prepare for specialization with additional diffusion tensor * made static methods const * put traits into internal namespace
[localevaluation.swipdg]
* use common function for default_beta, inner_sigma and boundary_sigma
* prepare for specialization with additional diffusion tensor
* made static methods const
* put traits into internal namespace

BarbaraV/dune-gdt,ftalbrecht/dune-gdt