Merge branch 'feature/hyperelastic' into 'master'

CHANGELOG.md

doc/doxygen/dumux.bib

doc/doxygen/groups/models.md

dumux/geomechanics/CMakeLists.txt

dumux/geomechanics/elastic/model.hh

dumux/geomechanics/hyperelastic/CMakeLists.txt

dumux/geomechanics/hyperelastic/localresidual.hh

dumux/geomechanics/hyperelastic/model.hh

dumux/geomechanics/hyperelastic/spatialparams.hh

dumux/geomechanics/hyperelastic/volumevariables.hh

test/geomechanics/CMakeLists.txt

test/geomechanics/hyperelastic/CMakeLists.txt

test/geomechanics/hyperelastic/main.cc

test/geomechanics/hyperelastic/params.input

test/geomechanics/hyperelastic/problem.hh

test/geomechanics/hyperelastic/properties.hh

test/references/test_hyperelastic_box-reference.vtu