[ci] Add gitlab-ci.yml to enable ci

Strategy:

1. Precompile docker container without dumux or dumux-lecture (the modules you want to test)
2. Globally define link to dunecontrol
3. Start first stage (build) with script to build dumux/dumux-lecture. Copy/Link/Move files to /builds/* as artifacts can apparently only be copied from within local "gitlab-dir"
4. Start second stage (test) with dependency on (build). Dependency enforces the unpacking of previously defined artifacts. (this is not working yet)

left todos

• nicer call of scripts
• update to only test dumux-lecture in lecture maybe dumux + lecture for dumux
• enable artifacts (nicer way of caching) pass between stages
• check timing (docker container seems fine, cache pre-build status?)
• check disk-space on behandla and cpus for pipelines
• unify buildbot and CI docker images?
• use other docker image than phusion?
• ...