Updates Dockerfile: Ubuntu 14.04 is used, redis, mysql and postgresql were removed (not needed).
Moves mysql, redis and postgresql to optional dependencies section. Postgresql version number was updated from 9.1 to 9.3 (Available in Ubuntu 14.04).
Removes out-commented apt-get line - adds upgrade command for apt-get.
Use double comments for commenting text in optional dependencies section.
Merge pull request #103 from stefan-it/stefan/dockerfile-update

Dockerfile update
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
Fixed docker script, now docker image uses /sbin/init which properly starts all services
Pass build_method as CI_BUILD_METHOD
Pass CI_PROJECT_DIR to WORKER
Fixed shell-based projects support