... instead of binding to LocalFiniteElement objects.

This is how binding works everywhere else, too.  In addition,
in frees us from the difficult task to always get the
appropriate LocalFiniteElement objects to bind to.

... instead of always constructing a local LocalGeodesicFEFunction
object. This makes the class consistent with all similar assemblers.
It also removes the hardwired 'geodesic' interpolation rule.

Unfortunately, this commit contains a bit of whitespace change.

Because it was way more boilerplate code than actual code.

This is what the other energies do.

This is the basis used as interpolation weights (for geodesic
FE functions) or for interpolating in the embedding space
(for projection-based FE functions).  The basis is not actually
used yet, but it needs to be given to the class in the
constructor.

Rather than constructing objects locally.

Rather, expect them as constructor arguments.

Instead, expect to be given one from the outside.  This is one
more step towards making local interpolation rules more like
local functions.

As one further step towards making LocalInterpolationRules
more like (local) functions, introduce a new method 'bind'
accepting a local finite element and a set of (local)
coefficients.  This method replaces the constructor
taking the same arguments. Instead, the local function object
now has to be default constructed.  This is just an
intermediate step, however.

Instead of hard-coding LocalGeodesicFEFunction.

MixedGFEAssembler is not part of an inheritance hierarchy.

It doesn't look like this code ever worked.

There is a generic mechanism for surface loads in form of the
NeumannEnergy class (to be replaced soon(TM) by something
even more generic).  This is what should be used, instead
of ad hoc implementations such as the one in SimoFoxEnergy.

Because it is an energy, not a local stiffness.

Rather than a LocalFiniteElement.  This makes LocalGeodesicFEFunction
more like a dune-functions-style local function, which I think
it should be.

Rather than a LocalFiniteElement.  This makes LocalGeodesicFEFunction
more like a dune-functions-style local function, which I think
it should be.

This patch contains only whitespace changes.

Previously, some code was in Dune::GFE, some was in Dune::,
and a lot of it was in the global namespace.

I wrote them years ago mainly because I thought they should exist.
But they were never actually used them for anything, and I don't
really know were they could be used either.  Supposedly they
could be useful for implementing problems without a minimization
formulation, but that's not currently planned, and I don't know
what the precise requirements would be, either.

Since the code is short and almost trivial, and easily resurrected,
this commit removes the two files.  For newcomers this will mean
two less files to wonder about.

It is default-implemented in LocalDensity itself, and therefore
density implementations don't have to implement it themselves
unless they need to do something nonstandard.

Rather than just on the type for points in the domain.
The point type is not enough: For example, if the density involves
a coefficient function given as a GridView function, then the
density has to be able to bind the local coefficient function
to the correct element, for which it has to know the element type.

Integration domains can be elements (i.e., Codim<0>::Entity)
or Intersections.

The actual bind method will follow in a separate commit.

This allows to fix the incorrect coordinate type that was expected
for evaluating the density.

Currently, densities only get the type used for coordinates
of the integration domain.  However, this is not enough:
The complete domain must be known, and this domain can be either
a grid element or a grid intersection.

As a first small step, this patch introduces ElementOrIntersection
as a template parameter of the CosseratShellDensity class.

This is one step towards turning SurfaceCosseratEnergy into a
generic SurfaceIntegralEnergy class.

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.

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

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.

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).

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

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

Rather than keeping a duplicate implementation of the bulk
Cosserat density.

Energies of particular models should not implement external loads
themselves, because that would lead to a lot of code duplication
(and possible inconsistencies).  A one step towards that goal,
allow to construct a CosseratEnergyLocalStiffness object
without external loads.