[md][box] Internal Dirichlet

* Set off-diagonal matrix blocks to zero if internal Dirichlet is set
* use correct problem() function in md framework
4 jobs for !2637 with feature/box-multidomain-internal-dirichlet
latest detached
Status Name Job ID Coverage
  Trigger
manual full-dune-2.7-clang
manual full-dune-2.7-gcc
manual minimal-dune-2.7-gcc
 
  Downstream Modules
created trigger lecture