sound sink option

[totaam]

Instead of using the XPRA_SOUND_SINK="autoaudiosink" xpra attach .., it would be nice to have a command line switch + config option instead. That way we could use "auto" on problematic platforms like Debian Wheezy, which helps for #1275.

[totaam]

For now, we check harder that pulseaudio is running before trying to use "pulsesink", if it isn't we'll use "autoaudiosink".

[totaam]

Also probably makes sense to be able to specify which device to use at the same time, something like: --sound-source=pulse:device=Built-in Audio Analog Stereo and --sound-monitor=pulse:device=Monitor of Built-in Audio Analog Stereo.