The NonplanarCosseratShellEnergy class contains a reimplementation of
the energy density of CosseratShellDensity.  The code is much easier
to understand and maintain if the density implementation of
CosseratShellDensity is used instead.

... and with constant Lamé parameters.  In many applications
there are constant, and it is convenient to be able to exploit that.

For some reason there were two code paths for the creation of the
solver object: One for dim==dimworld, and one for dim!=dimworld.
These shouldn't really differ, though, and indeed they didn't
as far as I can tell.  Theremore, merge the two code paths.

That is one step towards splitting off the energy density
into a separate class.

Also, it helps to unify the code paths for the different grid dimensions
in cosserat-continuum.cc

And use it in the dim==dimworld part of cosserat-continuum.cc.

For this test to be really helpful it has to use curved grids.

In the code that takes the initial iterate from a while, a call
to 'interpolate' was out-commented, because interpolating an
'EmbeddedGlobalGFEFunction' was not possible back in the days.

That has changed so, and 'interpolate' can now be called.
I still doubt that the code ever worked or works now.
How could it ever be tested?

'#	geändert:       src/cosserat-continuum.cc

This should simplify the code, but it doesn't: Computing the
displacement still needs a lot of code lines.

Just like in cosserat-continuum.cc, there is now a Python class
that implements the initial iterate and the Dirichlet boundary values
at the same time.

This reflects better what the file does.

Rather than hardcoding a straight reference configuration

This is more flexible, and more consistent with what
cosserat-continuum.cc does.

That is simply more flexible than the old parametertree format.

It is required by dune-fufem anyway.

In particular, there is a directory dune/elasticy/densities now.

The ugly preprocessor switch is still there, but I think
the method is more readable now.

The BulkCosseratDensity class implements three types of curvature
tensors. Previously, the preprocessor was used to select the one
to be actually used.  This patches removes the preprocessors checks
and implements run-time switches instead.

Because the part that computes the curvature energy from the
wryness tensor is identical for all curvature tensors that appear
in this implementation.

Instead, use LocalIntegralEnergy and the newly introduced densities
for bulk models or planar shell models.

While doing so, give an error message when non-trivial volume loads
are requested.  I have no example file that actually uses them
at the moment, and just by looking at the code I find it hard to believe
that they actually worked.  Getting them to work will mean having
introduce a density for volume loads, which don't want to do
until I need them.

Since this is the last use of the CosseratEnergyLocalStiffness class,
this patch remove the entire class as well.

The test used CosseratEnergyLocalStiffness, which I am in the
process of getting rid of.  And since I eventually want to
get rid of GeodesicFEAssemblerWrapper too, it is not worth the time
to port the test.

... instead of the class CosseratEnergyLocalStiffness.  This is
one step in the quest to get rid of CosseratEnergyLocalStiffness
entirely.

It does not use the main class CosseratEnergyLocalStiffness,
but only the small helper class to access local finite elements
from different types of basis trees.  I am not very happy about
this helper class, but let's be pragmatic and simply copy it
to nonplanarcosseratshellenergy.hh (with a new, unique name).

ADOL-C really only has fmin.  I don't know why this worked before.

The old implementation relied on assignment of FieldMatrix
from scalar, and for some strange reason that stopped working.

* I did not really test a lot of useful stuff.
* The class CosseratLocalEnergyStiffness is deprecated anyway.
* It stopped compiling and I don't know why.

This removes one use of the CosseratEnergyLocalStiffness class,
which is scheduled for complete removal.

If the grid is 2d we know that determinant is equal to
the determinant of the upper-left 2x2 block.

This extracts the density of the Birsan/Neff Cosserat shell model
with planar reference configuration from the CosseratEnergyStiffness
class.

Even though we know that it is always '3'.  Still, using gridDim
whenever that is meant is more expressive than '3'.

That way, we can also set the initial microrotation -- previously
it was hard-wired to the identity matrix.

Being able to explicitly choose the initial microrotation allows
to start, in particular, from a twisted strip.