Modernize rod code

Otherwise the Cosserat rod code will not compile without dune-parmg.

This reflect the current purpose of the test much better.

So far, the Cosserat rod energy implementation hat a first-order
finite element space hardcoded.  This patch removes that restriction.
As for the other models in this Dune module, the finite element basis
is now a template parameter of the model energy, and can be set to
any reasonable basis.

It is not a 'stiffness' anymore, but really only implements the
energy.

This is a prerequisite to a) support for higher-order FE,
and b) getting rid of the hand-written CosseratVTKWriter.

Previously, the rod3d code used a hand-implemented first derivative
of the rod energy, and FD for the second derivatives.  This patch
replaces this by ADOL-C for both first and second derivatives.
Advantages are:
* The code is much shorter, and easier to understand.
* The previous code contained interpolation formulae for
  first-order 1d geodesic finite elements.  This restricted
  rod problems to first-order GFE.  A follow-up patch will
  allow higher-order approximations.
* The new code runs roughly twice as fast.

GeodesicFEAssembler can replace it without problems.

As a first step towards getting rid of the RodAssembler class,
this patch moves the getStrain, getStress, and getResultantForce
methods to the RodLocalStiffness class.  I am not 100% convinced
that that is the best place for them, but I can't think of a
better one right now.

ADOL-C implements most standard math functions for its
'adouble' type, and they are not in the namespace 'std'.
dune-fufem contains a file adolcnamespaceinjections.hh
which imports some of these methods into the 'std'
namespace, but that is not the proper way to do it.
Rather, they should be found by argument-dependent
lookup (ADL), that is

  using std::sin;
  auto v = sin(x);

In the 'mixed' case the volume term was simply forgotten, and not
actually handed to the assembler.

It is very unlikely that somebody will use that ever again.

Rather than using a default file, which was the case previously.

Otherwise the program aborts for the usual mysterious reasons.