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/thumbbrowserentrybase.h

@@ -22,6 +22,7 @@
 #include <gtkmm.h>
 #include "lwbuttonset.h"
 #include "thumbnail.h"
+#include "guiutils.h"
 
 class ThumbBrowserBase;
 class ThumbBrowserEntryBase {
@@ -42,7 +43,7 @@ protected:
     int lowerMargin;
 
     
-    Glib::RWLock lockRW;  // Locks access to all image thumb changing actions
+    MyRWMutex lockRW;  // Locks access to all image thumb changing actions
 
     guint8* preview;  // holds the preview image. used in updateBackBuffer. TODO Olli: Make a cache to reduce mem significantly