Merge branch 'feature/sumfact-poisson' into 'master'

python/dune/perftool/error.py

python/dune/perftool/sumfact/__init__.py

python/dune/perftool/sumfact/amatrix.py

python/dune/perftool/sumfact/basis.py

python/dune/perftool/sumfact/quadrature.py

python/dune/perftool/sumfact/sumfact.py

test/sumfact/poisson/CMakeLists.txt

test/sumfact/poisson/poisson_dg_only_volume.mini

test/sumfact/poisson/poisson_dg_only_volume.ufl

test/sumfact/poisson/poisson_order1.mini

test/sumfact/poisson/poisson_order1.ufl

test/sumfact/poisson/poisson_order2.mini

test/sumfact/poisson/poisson_order2.ufl