Use continuous integration which is supported by GitLab

I think it would increases developers and users work if this repository uses a CI which is supported by the GitLab webinterface. Then anyone would see e.g. at first sight if the code in the repository is builable.

The currently supported CIs are:

• Atlassian Bamboo CI
• Buildkite
• GitLab CI
• Jenkins CI
• JetBrains TeamCity CI

For reference, the old issue is here.

Client issue

Server issue