Go support

For upcoming GitLab SR we need Go language support, because one GitLab service is written in this language:

https://gitlab.com/gitlab-org/gitlab-workhorse

Here we provide golang component, and helloweb-go service integrated into helloworld SR.

The patches are based on recent helloworld & helloweb restructuring (see !23 (merged) ).

Thanks beforehand for feedback,
Kirill

/cc @jerome, @kazuhiko, @rafael, @alain.takoudjou
/cc @gabriel, @Camata