Add Gitlab CI configuration

This commit adds a .gitlab-ci.yml file, which uses a feature
to fetch the config from a centralized repository. The intent is
to have all the gstreamer modules use the same configuration.

The configuration is currently hosted at the gst-ci repository
under the gitlab/ci_template.yml path.

Part of gstreamer/gstreamer-project#29
2 jobs for alatiera/include-everywhere in 3 minutes and 37 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Manifest
passed manifest #42754

00:01:14

 
  Build
passed build fedora x86_64 #42755

00:02:22