GitLab

* Update Dockerfile for base image
* Bump Docker base image to v1.2
* Update version info in README.md
* Update CHANGELOG.md

Updates to the dune-randomfield master branch made it incompatible with
the current version of DORiE. Allow the 'prep' stage to fail until there
is a resolution found.

* Install package `python3-vtk7`.
* Disable command line prompts while installing packages.
* Do not install recommended packages.

* Install python3-vtk7 non-interactively.
* Install libxt-dev to see if this suffices.

Image version now obeys semantic versioning, to allow for changes which
are not backwards compatible. Notice that the image version now has no
relation to the DUNE version.

Use the regular find algorithm and define a custom imported target.

This effectively reverts the last three commits.

* Fix ci build
Signed-off-by: Santiago Ospina <santiago.ospina@iup.uni-heidelberg.de>

* Documented and renamed norm for jumps in vector spaces.
* Remove bool from prepossesor definition fo the test.
Signed-off-by: Santiago Ospina <santiago.ospina@iup.uni-heidelberg.de>

* Fix CMake flags in CI.
Signed-off-by: Santiago Ospina <santiago.ospina@iup.uni-heidelberg.de>

* Test jumps in system tests.
Signed-off-by: Santiago Ospina <santiago.ospina@iup.uni-heidelberg.de>

* Added test for conforming jumps in normal direction of the skeleton grid.
Signed-off-by: Santiago Ospina <santiago.ospina@iup.uni-heidelberg.de>

Reduce number of CPUs available to DIND runner

* Add target 'unit_tests_parallel'
* Add two new tests executing two grid creation tests in parallel
* Update names of grid creation ini files
* Fix bug in test-grid-creation.cc that prevented parallel execution
* Add parallel unit tests to existing parallel test job
    and rename it to 'test:parallel'

* Add standard YAML file with parameters for sand and silt.
* Modify create_param_maps.py for creating an H5 datafile with maps
    for tests.
* Add a new target 'prepare_testing' for creating the H5 datafile
    before running system or unit tests. It is a dependency of
    'system_tests' and 'unit_tests' (but not 'test').
* Add gitignore exception for H5 datafile.
* Remove creation of H5 datafile from GitLab CI config.