Queue state verbose, fixes #4058

Improvement to the Batch Queue:
- Start Queue/Stop Queue checkboxes replaced with one swith.
- It is now immediately clear whether the queue is running or not.
- The queue is visually stopped once it is empty.
- String keys fixed to use BATCHQUEUE_ prefix instead of FILEBROWSER_.

rtgui/batchqueuepanel.h

@@ -32,13 +32,12 @@ class BatchQueuePanel : public Gtk::VBox,
     public FormatChangeListener
 {
 
+    Gtk::Label* qLbl;
     Gtk::Button* zoomInButton;
     Gtk::Button* zoomOutButton;
-    Gtk::ToggleButton* start;
-    Gtk::ToggleButton* stop;
-    Gtk::CheckButton* autoStart;
-    sigc::connection startConnection;
-    sigc::connection stopConnection;
+    Gtk::Switch* qStartStop;
+    sigc::connection qStartStopConn;
+    Gtk::CheckButton* qAutoStart;
 
     Gtk::Entry* outdirTemplate;
     MyFileChooserButton* outdirFolder;
@@ -69,6 +68,7 @@ public:
 
     void startBatchProc ();
     void stopBatchProc ();
+    void startOrStopBatchProc();
 
     void saveOptions ();
     void pathFolderChanged ();