Merge pull request #162 from espressomd/github_actions

.github/actions/docker/Dockerfile

.github/actions/docker/action.yml

.github/actions/docker/entrypoint.sh

.github/workflows/build.yml

.gitignore

.gitlab-ci.yml

README.md

docker/Dockerfile-centos

docker/Dockerfile-clang

docker/Dockerfile-debian

docker/Dockerfile-fedora

docker/Dockerfile-opensuse

docker/Dockerfile-rocm

docker/Dockerfile-ubuntu-18.04

docker/Dockerfile-ubuntu-19.04

docker/Dockerfile-ubuntu-20.04

docker/Dockerfile-ubuntu-cuda-10.1

docker/Dockerfile-ubuntu-cuda-9.0

docker/Dockerfile-ubuntu-min_boost

docker/Dockerfile-ubuntu-travis