Merge branch 'feature/diameter-handler' into 'master'

applications/convection_diffusion/conv_diff_dg.ufl

applications/poisson_dg/poisson_dg.ufl

python/dune/perftool/loopy/mangler.py

python/dune/perftool/loopy/target.py

python/dune/perftool/pdelab/__init__.py

python/dune/perftool/pdelab/geometry.py

python/dune/perftool/ufl/preprocess.py

python/dune/perftool/ufl/visitor.py

test/poisson/opcount_poisson_dg.ufl

test/poisson/poisson_dg.ufl

test/poisson/poisson_dg_neumann.ufl

test/poisson/poisson_dg_tensor.ufl