Piotr's Tutorial 7 on hyperbolic problems

See merge request !38

Bugfix/fix typo

See merge request pdelab/dune-pdelab-tutorials!40

two hats above x in integral dx, and correction of g_T(m)

Necessary cleanup for warning-free work with 2.6

See merge request !37

fixed misplaced iterator

See merge request !39

Note this implies a semantic change, as previously the interval
was divided into 2^subsampling intervals. Now the explicit number
of intervals is set.

It does not exist anymore.

Merge branch 'Piotr/tutorial07' of http://gitlab.dune-project.org/pdelab/dune-pdelab-tutorials into Piotr/tutorial07

Use referenceElements directly from dune-geometry

See merge request !36