waitress: Close connection if body has been received

Now libwaitress won’t wait until the server closes the connection if the
request body has been received. Multiple requests per connection are not
supported anyway. Fixes #321. Thanks to Michael Stowe.
Permit multiple HTTP errors in a row

1) Make sure that multiple bad playlists in a row don’t result in a
   temporary ban
2) Ignore songs skipped because the playlist timed out after pausing for
   too long