Also introduce default output format and selected device format, should the
user want another format.
As part of this, change enum player_format in player.h to enum media_format in
misc.h so that it is akin to struct media_quality.
Modify json API to support this.
Roku SoundBridge devices can be treated as dumb speakers; they offer a
texted based protocol, RCP, that allows the server to request the Roku
device to connect to the server's stream.mp3 and provides ability to
control volume
Roku devices appear as speakers automatically via mDNS announcements on
the server _roku-rcp._tcp
