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.

- 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

[WIP]: Addons to dumux are stored in dumux-addon and are also installed into a dumux-addon directory

- 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