Add a simple CLI interface to project

[bitfoo1]

It would be nice to have a simple command line interface to initialise a gcip pipeline with a sample gitlab-ci.yml.
And to validate if the generated-config.yml which is used to drive the subsequent pipeline.

[ThomasSteinbach]

This could then be packaged into the Dockerfile and be called like

docker run --rm gcip init > .gitlab-ci.py