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