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.

GeodesicFEAssembler can replace it without problems.

Do this by making RodAssembler more similar to the generic
GeodesicFEAssembler: the constructor argument is now a
general LocalGeodesicFEStiffness, and not something particular
to rod problems.

And make it actually test something.

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

[[Imported from SVN: r9614]]

[[Imported from SVN: r8349]]

[[Imported from SVN: r6305]]

[[Imported from SVN: r5940]]

[[Imported from SVN: r2010]]