This replaces the dedicated implementation of the quadrature loop
for harmonic energies -- that is not needed anymore.

In particular this means that the test for it can be removed.
In theory it should be replaced with a test for the harmonic
energy *density*, but that density implementation is so short
that it doesn't really require a separate test.

The new method is Fufem::markBoundaryPatchDofs, which apparently
works in just the same way.

It was apparently not used.

If you should ever need something like this in the future,
please use periodicbasis.hh from dune-functions.

There are two important changes:  First of all, the new class implements
the `dune-functions` interface rather than the deprecated one based
on inheritance from `VirtualGridViewFunction`. Secondly, the new class
does not hard-wire geodesic interpolation anymore.  Rather, you can
give it interpolation classes which then govern how interpolation is done.

This change was long overdue.  It was now needed to make
gradient-flow.cc compile with the post 2.9 version of dune-fufem again.

Because it really is only an energy.

Because it is not a stiffness, it is really just an energy.

Previously, they all inherited from LocalGeodesicFEStiffness,
which was weird, because none of them implemented first or
second derivatives as you would expect from something called
'stiffness'.

The code it contains is adolcnamespaceinjections.hh.

Capturing any polymorphic object by value is wrong,
and gcc 8 started to warn about this in the case
of exceptions.

The latter is deprecated as of dune-functions 2.6.

This is needed to build with a recent dune-common and dune-fufem

Otherwise some dune-common stuff will not work properly,
for example copying of FieldMatrices that use adouble
as their number type.

It has been removed from dune-functions in the last release
(at least).

You never know, we may be doing dim!=dimworld grids eventually.

Of course we always need unitvector.hh.  vtkadapter.hh, on the other hand, only
exists in dune-functions 2.4.

This is needed even though we don't actually use MPI here.  Dune aborts with a
run-time error otherwise.

That should work when calling the executable from 'build-cmake/src'.

This initial commit simply brings a cleaned-up version of the harmonicmaps program.
The first step will be to make it compute curve-shortening flow on the sphere.