The ProductManifold class generalizes RigidBodyMotion, and can do
everything that the RigidBodyMotion class can.  Therefore there is
no point in keeping RigidBodyMotion any longer.  Having two
implementations for the same thing will just confuse people.

This is needed to actually compare the 3D-model with the 2D-approximation

In particular, we move the test for the computeDR method from
cosseratenergytest.cc to here.  It is a method that does not
have anything to do with Cosserat mechanics directly.

The test still seems overly complicated.  Do I really need
a LocalGeodesicFEFunction?  Maybe I can simplify it later.

* Do not test with configurations that result in zero-area elements
  (because the energy is inf in these cases).
* Test for the relative energy difference, rather than the absolute one,
  because the energy values can get very large.

It is not clear what this method was supposed to test,
because the CosseratEnergyStiffness class does not
actually implement a the gradient.

To prevent confusion with a class of the same name in
dune-localfunctions.

All of a sudden it gets confused with a class of the same name
in dune-localfunctions.

The latter is deprecated as of dune-functions 2.6.

In particular, this patch removes tests for the gradient
of the Cosserat energy and related things.  The
CosseratEnergyLocalStiffness class stopped computing
these things back in 2014 (in 63e42ece )
when it was decided that algorithmic differentiation was
the way to go.

With this patch, the test builds again, but it doesn't run yet.
I am afraid that fixing that may require a larger investment
of time...

[[Imported from SVN: r8631]]

[[Imported from SVN: r8628]]

[[Imported from SVN: r8597]]

space of orthogonal matrices.

[[Imported from SVN: r8573]]

[[Imported from SVN: r8460]]

[[Imported from SVN: r8404]]

[[Imported from SVN: r8402]]

[[Imported from SVN: r8401]]

[[Imported from SVN: r8400]]

[[Imported from SVN: r8399]]

[[Imported from SVN: r8381]]

[[Imported from SVN: r8182]]

[[Imported from SVN: r8150]]

[[Imported from SVN: r8057]]

[[Imported from SVN: r8056]]

[[Imported from SVN: r8055]]

[[Imported from SVN: r8052]]

This is needed to test quad elements and higher-order gfe.

[[Imported from SVN: r8047]]

[[Imported from SVN: r7996]]

[[Imported from SVN: r7613]]