some enhancements of the Fast Export functionality

- remember fast export options across RT sessions

- added option to use a dedicated "Fast Export" pipeline, trading speed for
  quality (resizes early instead of at the end)

rtengine/processingjob.h

@@ -49,6 +49,8 @@ public:
             initialImage->decreaseRef();
         }
     }
+
+    bool fastPipeline() const { return fast; }
 };
 
 }