Ability to re-order mixer channels

In the Fx Mixer View, you can select a channel and press Alt+Left
and Alt+Right respectively to re-order Fx Channels. This should be
made more easily available in the GUI eventually.

include/FxMixerView.h

@@ -87,6 +87,10 @@ public:
 	// notify the view that an fx channel was deleted
 	void deleteChannel(int index);
 
+	// move the channel to the left or right
+	void moveChannelLeft(int index);
+	void moveChannelRight(int index);
+
 private slots:
 	void updateFaders();
 	void addNewChannel();