Couple with Gitlab-Repo

[jakob-fritz]

Mirror repository with Gitlab-Repo so that CI can use HPC-Resources. This is helpful e.g. for running GPU-Tests and/or for running Benchmarks.

Tasks that should be done:

• [x] Mirror with Gitlab for new pushes
• [x] Mirror also for updated Pull-Requests (only if certain tags are set and people with appropriate permissions triggered CI)
• [x] Run tests on HPC (e.g. GPU-Tests)
• [ ] Get back Reports (e.g. coverage) from Gitlab and include in Github-Statistics

[jakob-fritz]

#386 Works on this