Fix and simplify setup

[wolfgangmm]

• Incorporates most of the changes/updates suggested in PR update files to match our recent docker-compose standards #7 by @chakl
• Omits some configuration steps by parametrizing settings in docker-compose.yml. Building a single xar app is now possible without editing the Dockerfile
• Use nginx templates. Modifying the nginx configuration is no longer required for the default setup. No more search & replace in files

Not having to fiddle with configuration files makes the process much faster, smoother and less error prone.

[duncdrum]

LGTM