Docker refactoring

[chreman]

This PR is a refactoring/enhancement of the dockerized API layer and includes following changes:

• Make Docker-containers more configurable
  • Move files that are used within containers to their respective folders
  • Port that API container is listening on is now a configurable env variable
  • Dataprocessing, getPapers containers and API container now take parameter for redis-host (and redis-port) from env
  • API container should take parameter for pgsql-host and -port, flask-API now reads pgsql info from env
• Get rid of network mode “host” and use docker-networks (service resolution) instead
• Change how containers are built:
  • Tag built docker-images with the git commit ID they were built from
  • Make compose-file aware of explicit container versions/hashes
• Tell the nginx-proxy in the about multiple flavors of similar services in docker-compose
• Separate volumes for postgres containers
• Add some endpoint /api/service_version that reads SERVICE_VERSION from env and returns a json object from the container
• Break flask-app in two and split off persistence layer
  • Re-route persistence requests from api-app via a new namespace/endpoint to the persistence-app in a different container (but same flavor)
• Prepare for higher load:
  • Add some rate-limiting for API requests or max_n concurrent connections (bots, one-user saturation, workshop-peaks)
  • in legacy code: wrap performCalculation - done
  • in Api code: on service-access level: check queue length, return status message and error reason - done
• Create a lightweight-PHP apiclient as PHP class that is re-usable in search.php and the various GET phps