UI: Sort audio controls by source name

Audio controls in OBS Mixer and Advanced Audio Properties window are not
sorted at all.  Every time OBS is restarted they get shuffled (Jim note:
This is due to json object hashing).  The order of these controls is
additionally not consistent between the mixer and the advanced audio
properties window.

Closes obsproject/obs-studio#1242

UI/adv-audio-control.hpp

@@ -51,6 +51,7 @@ public:
 	virtual ~OBSAdvAudioCtrl();
 
 	inline obs_source_t *GetSource() const {return source;}
+	void ShowAudioControl(QGridLayout *layout);
 
 public slots:
 	void SourceFlagsChanged(uint32_t flags);