This is an important step towards making the 'mixed' Cosserat code more like
the regular one.  The mid-term goal is to merge the two implementations, because
there is way too much code duplication here.

The DR variable (the derivative of the microrotation R wrt space) had dimensions 3x3x3.
This is two big in a shell context, because there are actually only two space dimensions.
Hence the correct size is 3x3xgridDim.

The results without this patch were not wrong, though, only a bit wasteful.

This makes 2nd-order orientation functions work again.

The implemented formula was actually for the projection of Stiefel manifolds, of which
the orthogonal matrices are only a special case.  For this special case, one term
drops out and doesn't have to be implemented.

This marks the last step of porting the 'cosserat-continuum' application away
from the dune-fufem bases.  One must not(!!!) mix dune-fufem bases with
dune-functions bases, as they use different dof orderings at least in the P2 case.

Because this object doesn't exist in dune-functions bases anymore.

[cleanup] Move the FD approximation of the GFE function gradient from the GFE function into the test

It is a part of the test harness, and should not clutter the implementation of the
GFE functions themselves.

Needed for projection-based finite elements.

This patch also adds a unit test.  So far this test passes.

PQKNodalBasis has been renamed to PQkNodalBasis