Partially solving issue 1788: "Crashing during processing of queue"

It also correct a bug of wrong image orientation (was wrong in the File Browser while good in the Editor tab)

This patch also introduce several speed optimizations like:
   - switch between File Browser and Editor tab in Single Editor mode
   - asynchronous computation of the Batch Queue's thumbnails
   - quick start of RT even with a huge queue
   - less GUI overhead when applying a profile to multiple thumbs in the File Browser

rtgui/lwbutton.h

@@ -25,6 +25,7 @@ class LWButton;
 class LWButtonListener {
 
     public:
+        virtual ~LWButtonListener () {}
         virtual void buttonPressed (LWButton* button, int actionCode, void* actionData) {}
         virtual void redrawNeeded  (LWButton* button) {}
 };