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)

rtgui/options.h

@@ -279,6 +279,7 @@ public:
     int           fastexport_resize_dataspec;
     int           fastexport_resize_width;
     int           fastexport_resize_height;
+    bool fastexport_use_fast_pipeline;
 
     // Dialog settings
     Glib::ustring lastIccDir;