replaced user setup

- Added a new setup system featuring:
  - Suport for multiple users in single docker run
  - Map any uid or gid to a sftp username of your choice
  - Easy syntax, using the familiar old env vars
- Minimized log spam, showing messages only when necessary
- Removed sftpusers in favor of forcing sftp on all
- Switched from shared home, to user specific,
  (more volumes in exchange for flexibility)