Improve the setup script

Description

• Improve the documentation
• Add handling short and long options
• New options:
  • --help shows the help
  • -h|--host=HOST sets the hostname
  • --protocol=PROTOCOL sets the protocol
• All the configured files are now in the "funkwhale" directory (so that all the containers are prefixed with "funkwhale")
• The final message points to the reverse-proxy configuration