Add Julia support through the .gitlab-ci.yml template

Merged username-removed-270429 requested to merge (removed):6-julia-template into master

Added support for testing Julia packages via the GitLab CI framework.

Added support includes:

  1. Testing the package in different Julia versions,
  2. (optionally) Reporting code coverage results.

Related to gitlab-org/gitlab-ce#22040. Fixes #6 (closed). Closes #6 (closed)