Make the order hint optional
Ditch sumbmodules and use a NuGet package for Espera.Network
Refactor the broadcast code
Update Newtonsoft.Json
Initial hack on the file transfer API
Properly find a matching message and file transfer client

Fixes #64

Previously, if a user disconnected and reconnected again, the ReplaySubject would replay every client again and the selector would select the first (disconnected) in the sequence