Merge branch 'update-gitlab-ci' into 'master'

Update GitLab CI configuration

*Description of changes*

Update GitLab CI. After reading [GitLab's blog post](https://about.gitlab.com/2016/07/29/the-basics-of-gitlab-ci/) about their CI system, it seems that we can easily start generating build artifacts for PRs and regular pushes.

*Related to:*  N/A

See merge request !111