Just move and rename the namespace.

- Rename to better reflect the contained date.
- Expected solution update due to output of specific flux instead of flux.

- Rename to better reflect the contained date.
- Expected solution update due to output of specific flux instead of flux.

- Rename to better reflect the contained date.
- Expected solution update due to output of specific flux instead of flux.

- Rename to better reflect the contained date.
- Expected solution update due to output of specific flux instead of flux.

- Rename to better reflect the contained date.
- Expected solution update due to output of specific flux instead of flux.

- Rename to better reflect the contained date.
- Expected solution update due to output of specific flux instead of flux.

- Rename to better reflect the contained date.
- Expected solution update due to output of specific flux instead of flux.

- Rename to better reflect the contained date.
- Expected solution update due to output of specific flux instead of flux.

- Rename to better reflect the contained date.
- Expected solution update due to output of specific flux instead of flux.

Rename to better reflect the information stored in the data_array.

The truncated version is not exactly comparable with the
coordinate transformation version and results deviate by
10^-7. Better to use accurate representation of the tensor
for the comparisons.

clang-tidy modernize-use-emplace check.

clang-tidy modernize-use-using check.

clang-tidy modernize-loop-convert check.

clang-tidy modernize-use-override check.

clang-tidy modernize-use-default-member-init check

Also those where the second and so forth arguments are defaulted.

The MathLib::TemplateVector3 is an exception, because of the many
required changes through the code, which relies on the implicit
conversion from TemplatePoint<T, 3> to TemplateVector3<T>.

clang-tidy '*explicit*' check.

Generation of the pvd files is not (yet) implemented,
but easily possible with an one-liner:

sed 's/RichardsFlow_2d_small/Richards_2d_geometry_OBSERVATION_POINT/g' RichardsFlow_2d_small_pcs_0.pvd> Richards_2d_geometry_OBSERVATION_POINT_pcs_0.pvd