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
Use Observable.FromAsync
Omg whiteline
Add songs from a mobile device to the playlist
Wait on the data to arrive
Always push on a new task
Omgggggggggggggggg
Fix the song source serialization
Serialize the songs properly
Omfg
Merge pull request #77 from flagbug/file-transfer

Song transfer API