Merge branch 'gitlab-ci' into 'master'

Added gitlab-ci.yml for automated testing & fixed environment-cpu.yml

See merge request !11
1 job for master in 3 minutes and 57 seconds (queued for 54 seconds)
Name Stage Failure
test Test
# To deactivate an active environment, use
# $ conda deactivate

$ conda activate flatland-env
Could not find conda environment: flatland-env
You can list all discoverable environments with `conda info --envs`.

ERROR: Job failed: command terminated with exit code 1