Move software monitoring to audio configuration dialog

The local channel mute checkbox is easily confused with the "xmit" button.  "xmit" decides whether to send audio to the server.  Local channel mute decides wether to use software monitoring.  New users may not understand the distiction between these two types of mute.

The solution is simple: since software monitoring is a one-time setup that doesn't need to be changed during jamming, move the setting into the audio configuration dialog.  This makes the user interface simpler and eliminates confusion between local channel mute and xmit.