add custom identifiers, image optimisations

[realies]

• pin base image to a tested tag
• omit image upgrade
• reduce image size using --no-install-recommends
• satisfy machine-id app requests
• update internal folder mapping
• add optional user with configurable uid and gid to align mounted volume ownership
• reduce redundant layers
• satisfy X environment variables
• update readme to reflect changes, add badges
• update compose file to reflect changes
• add stuck X lock file fix
• reconfigure supervisord to store all logs in /tmp

fixes #5