A CMake macro called `add_precice_file_links` is added. If one
calls this macro in a `CMakeLists.txt` via `add_precice_file_links()`,
file links to all XML files in the directory of the `CMakeLists.txt`
are created.

The paths in tests have been adapted accordingly to use 
`CMAKE_CURRENT_BINARY_DIR` instead to refering to the source directory.

A lot of the codes for monolithic coupling are out of date
and make maintenance tedious. This commit removes the monolithic
coupling since the monolithic coupling is already implemented
in DuMuX and we do not need the adapted version of the monolithic
coupling here anymore.

We use prebuilt Docker images on the `ajaust` namespace and push them to DockerHub. This commit makes sure that the CI is using these new container images. These changes have been done while moving the CI to a new VM.

Related changes:

* Tolerance of partitioned tests was increased to `5e-5` as the results changed slightly using the new Docker images on the new VM.
* Added a copy of `fuzzycomparevtu.py` from the DuMuX repository into this repository. This allows us to be more independent of the location of the DuMuX repository.

- This MR removes unused test cases and separates stronger
between tests and example cases. Test cases and examples 
are classified as `monolithic` or `partitioned`.
- The tests have been adapted such that the build target
`build_tests` builds all necessary executables. This means
on can now run `make build_tests` from `build-cmake` and 
afterwards run all tests `ctest` to test the adapter.
- The CI has been adapted to make use of the new build 
process for tests.

For more information check out merge request: !18

- Python script driving the partitioned tests is no also running the diff and cleaning up the directory the test is running in.
- As a consequence the CMakeLists.txt for the tests (FVCA) could be simplified

- Python script driving the partitioned tests is no also running the diff and cleaning up the directory the test is running in.
- As a consequence the CMakeLists.txt for the tests (FVCA) could be simplified

- FVCA publication code moved to https://git.iws.uni-stuttgart.de/dumux-pub/jaust2020a
- This branch contains more than just the FVCA code and cleanup.
- Added some new examples for non-smooth coupling interfaces
- Added some new examples for 3D
- Monolithic coupling depends on special DuMuX branch
- Added CI
- Added code formatting