Remove whitespace in maxProximalNewtonSteps-string @Riemannianpnsolver (causes problem with get-method of parameterTree)

Various minor fixes and improvements

See merge request !154

Previously they were returned by value, but I do not remember any
actual reason for that.  Return by const reference leads to a
measurable speed increase when computing the derivatives of
projection-based FE onto the sphere.  It also fixed some
undefined behavior in that code, which took const-references
of the returned temporaries.

Returning the coefficients by const reference is more difficult
for product manifolds, because previously the interpolation rules
stored the coefficients separately for each factor space.
With this patch, these rules now store the coefficients twice:
once in the old separate format, and once as needed for returning
them by reference.  Interpolation rules are not meant to exist
in large numbers, and therefore I do not think that this
extra space consumption matters.

They were 'field_type' before, which is 'adouble' when used
together with ADOL-C (the typical case).  But using 'adouble'
for parameters is unnecessary and wasteful.

Fix nonconforming interpolation

See merge request !153

This broke recently (or never worked), because nonconforming
discretizations were not tested anywhere.  This patch therefore
also generalizes harmonicmaptest to also test with a
nonconforming discretization.

As part of the fix, the interpolation rules get a new method
`evaluateValueAndDerivative`, because the previous way to get
the value and the derivative in a single call (the `evaluateDerivative`
method that takes a value as an argument) only worked for the
conforming case.

This avoid two unsuccessful iterations at the beginning,
and hence reduces the overall time to run the test somewhat.

This is needed to support nonconforming discretizations.

Fix: Consistent naming of parameter strings

See merge request !152

Add option to choose a different Regularization-Norm for the Riemannian Newton with Hessian modification

See merge request !150

	The h1SemiNorm was only setup when the instrumented-flag was true.
	These are however independent functionalities.

MixedGFEAssembler: Pass local stiffness by r-value, l-value, shared_ptr

See merge request !151

They were expected to be the factors of a ProductManifold which is
also a template parameter.

Expecting the product and the factors is redundant.  We simply
extract the factors from the product now.

Previously, it expected two factor spaces, as separate template
parameters.  Taking a single ProductManifold type is more consistent
with GeodesicFEAssembler, and it allows to eventually generalize
the code to more factors, if desired.

... but disallow a plain pointer.  This increases consistency with the
GeodesicFEAssembler class.

Make BulkCosseratDensity interface more standard-like

See merge request !149

In the wake of this, remove all Cosserat nomenclature.

We keep the restriction to two factor spaces, because I see no
short-time need for more generality.

Not all densities depend on the function value (e.g., elasticity),
and not all of them depend on the derivative (e.g., dead volume loads).
If the TargetSpace is a product manifold, not every density depends
on all factors.  This commit introduces an interface that allows
the assembler to query what quantities of what factor a density
depends on, to skip GFE interpolation that are later unused.

dune-elasticity also has densities, but they implement a slightly
different interface.  Instead of having special code for such
densities in the LocalIntegralAssembler, add a wrapper that
makes densities from dune-elasticity look like dune-gfe densities.

Use the standard operator() method instead.

I don't see why this has to be kept after the migration.

Add missing regularization term in the quality measurement for step acceptance

See merge request !147

Use plain std::vector<double> for element energy gradients

See merge request !148

Non-composite settings use Dune::Matrix<double>,
composite settings use a FieldMatrix where each entry
is Dune::Matrix<double>.

This is not quite as simple as the dune-functions convention,
which is to use Dune::Matrix in all cases.  But it is still
simpler than before.

There is no point in testing assemblers that only exist in the test
itself.  Historically, they may have been useful when developing
the dune-gfe assembler framework because they were simpler (they
compute the Euclidean derivatives, not the Riemannian ones).
Nowadays, they just waste CPU cycles.