Test FTP Server Shell, fixes and finalization

Test FTP server

• Dockerfile, image availabe on Docker Hub
• Integrated shell
• Generic .NET Host

Fixes

• Issue #55 (Local port is queryable)
• Issue #56 (Better LIST output)
• File system UID/GID changes
• Fixed several causes of FTP client connection that stayed open
• EPSV 2: The 2 isn't the port, it's the address family (2=IPv6)

Changed

• Completed transition to piplines/channels
  • Switch to/from TLS works again
• Pausable services (FTP server, reading from network stream, etc....)
• PAM authentication module doesn't need .NET Core 3.0 any more
  • It'll only work on Linux for now