Configure deployment setup in yml instead of env vars

[baschny]

I currently can configure some stuff in a "project.yml" file, but the most important things like deploy_to, application, url, context etc can only be set via environment variables. So you need yet another "shell script wrapper" just to call the correct deployment target (which in our case is configured in "samson" GUI and not even versioned).

So my wish would be to only require two env-vars (DEPLOYMENT_PROJECT + some other switch - i.e. DEPLOYMENT_STAGE to keep the samson terminology) and with that all other variables are fetched from the relevant project file.

[mblaschke]

Added a new python based deployment wrapper with 29f3cb9 which should improve the situation. Still WIP

[mblaschke]

New deployment wrapper needs new samson-deployment image update, will be released with Dockerfiles 1.0