Merge branch 'feature/istl-solver-factory' into 'master'

CHANGELOG.md

dumux/common/loggingparametertree.hh

dumux/common/parameters.hh

dumux/linear/CMakeLists.txt

dumux/linear/istlsolverfactorybackend.hh

dumux/linear/solver.hh

test/common/parameters/test_loggingparametertree.cc

test/freeflow/shallowwater/dambreak/CMakeLists.txt

test/freeflow/shallowwater/dambreak/main.cc

test/freeflow/shallowwater/dambreak/params.input

test/freeflow/shallowwater/roughchannel/CMakeLists.txt

test/linear/params.input

test/linear/test_linearsolver.cc

test/porousmediumflow/richards/implicit/lens/main.cc

test/porousmediumflow/richards/implicit/lens/params.input