Support different versions of Go in the containerized version

[canthefason]

Currently, we only have support for Go Version 1.6.3. We need to extend it and add support for other versions, as well.

[julianxhokaxhiu]

I suggest to use tags, and automatically trigger the build process on Docker Hub. So if I need 1.6.3 I'll fetch the docker image with tag 1.6.3.

Of course if 1.6.x is still a living version, consider doing a branch per version, until it's considered deprecated.

By default, always consider the latest version. Thanks!