Merge branch 'fix/solver-factory-dune27' into 'master'

[linear][istlsolverfactorybackend] Fix compiler error for dune-2.7 and BCRS matrices

Closes #868 (closed)

See merge request !2017 (merged)

(cherry picked from commit c211d012)

dccae09f [linear][istlsolverfactorybackend] Fix compiler error for dune-2.7 and BCRS matrices