... rather than a LocalGeodesicFEStiffness.  That is a much
cleaner design -- A 'stiffness' produces first and second
derivatives for an 'energy'.

Currently, all implementations of variational problems inherit
from LocalGeodesicFEStiffness, which requires gradient and Hessian
implementations.  However, most of these implementations really
only implement the energy, and leave computations of first and
second derivatives to algorithmic differentiation.  To make
this clearer, this patch introduces an abstract base class
LocalEnergy for all implementations that really only have
an energy.

Throw out the AmiraMesh support instead.  I have not seen
anybody using Amira for years.

It combined computing rod configurations and their discretization
errors.  Nowadays the way to do that is to use rod3d.cc for the
rod configurations, and compute-disc-errors.cc for the errors.
Hence rod-eoc.cc is not needed anymore and can go.

.gitlab-ci.yml: use C++17 for GCC (for `if constexpr`)

See merge request !17

.gitlab-ci.yml: require Python 3

See merge request !19

Python 2's include files still contain the `register` keyword which is no longer allowed in C++17; using it is an error for clang.

Remove wrong template parameter (GradientRT) from usages of LocalFEStiffness in film-on-substrate

See merge request !18

To make it clear that that test does not currently test anything.

Previously, the layout of my computer's file system was
hard-coded here.

In this file they are not needed at all anymore.

Film on substrate

See merge request !13

Fix adolc and path

See merge request !15

When using ADOL-C together with MPI we need to use different tags in the
ADOL-C function calls for each process. If we use the same tag, then the
processes will interfere with each other causing undefined behaviour.

I forgot the GridFactory::createGrid did return a plain pointer
as recently as dune-grid 2.6.