Adds .gitlab-ci.yml, will run linting/build on merge request.

I've setup a gitlab runner in a box at UWA that we have privileged access to. It contains a GTX 980 so it should eventually be able to run a small test pipeline. I have set up a shared /artifacts/ folder on the host that jobs can save/load from, though the jobs must be tagged with 'spiir,gpu' to be delivered to our runner.

With this current .gitlab-ci.yml; on merge, a job should check for linting, and one should do a test build of the spiir Dockerfile.

Closes #9 (closed)