Adjust riemannian tr solver to upstream changes

See merge request !8

It does not look like that code is used anytime soon, so let's get rid
of it for the sake of tidyness.

It is no test.  Rather, it is a program I used to create illustrations
for the paper on GFE test functions (arXiv:1607.07479).  I moved the
program into the git repository of that paper.

This was never a real test.  Rather, it was I toy for me to test
a mathematical property of GFE functions which is known to be
false anyway.

That's already done in adolcnamespaceinjections.hh, in dune-fufem.

Update .gitlab-ci.yml for newer CI images

See merge request !14

This resolves a name ambiguity.

This to clang for pointing out the problem.  I had not noticed it before
because the code was only wrong for dimworld<3, which I never tried.

This makes sequential cosserat-continuum compile again.

OneDGrid does not have method leafbegin (anymore?)

See merge request !6

# Conflicts:
#   dune/gfe/geodesicfefunctionadaptor.hh

These two files are very similar, and merging them will reduce
maintenance effort in the future.  As of this patch, there is
now quite a number of preprocessor directives in the new merged
cosserat-continuum.cc.  That is not pretty, but the new state
is still much easier to maintain than two completely separate
files.  What is more, I hope to be able to reduce some of that
preprocessor trickery by smarter use of the dune-functions
basis trees.

This makes mixed-cosserat-continuum compile again.

This used to work only with dune-fufem bases, but the method
constructBoundaryDofs recently learned to also handle the bases
of dune-functions.

This used to be a yes/no, parameter, now we require 'cube'
rather that 'yes' or 'true'.

But keep compatibility with dune-grid 2.6 as well.

WARNING: These methods implement the projection in quaternion
space.  This is NOT the canonical projection in matrix space.

The original implementation measured the error of SO(3)-valued
functions in quaternion space in a few places.  This patch
converts another occurrence of this to matrix space.