rtp_player_dialog: Route audio for a stream to left/right speaker in RTP player

rtp_player_dialog: Route audio for a stream to left/right speaker in RTP player

Column 'Play' added to player. Double click on a stream in the column changes
audio routing for the stream.
When soundcard supports only one channel, there are Mute/Play option. When
soundcard supports two or more channels, there are Mute/L/L+R/R options.
Muted channel is drawn with dotted line.

Change-Id: If120c902195da46f98a1663c589f20c6a1da0ba7
Reviewed-on: https://code.wireshark.org/review/35687
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Tested-by: Petri Dish Buildbot
Reviewed-by: Anders Broman <a.broman58@gmail.com>