Resolve "migrate to podman"

• Migrate to container management tool podman
• Image for w2pegp containers are based on the latest version of web2py and on RPMs available in the alpine:edge distribution since July 2020:
  • python 3.8.5
  • gunicorn 20.0.4
  • matplotlib 3.3.1
  • pandas 1.0.5
  • web2py 2.20.4
• Image sizes are reduced by a factor by about 2.6
• It is deprecated to build w2pegp images by using web2py archive and conda
• Increase the timeout for gunicorn workers to 10 seconds
• Closes #6 (closed)