Enhanced GitLab CI runner to support running builds in Containers and on Virtual Machines

- Notify GitLab CI about supported languages, OSes and runner capabilities
- Added support for many concurrent workers
- Enhanced build script generation when using non-travis mode
- Allow to overwrite executor script. It allows to use script which uses Docker Container (run_docker_script) or Parallels Virtual Machine (run_pr_script)
- Track list of workers with received build_data