Add auto focal length for perspective in editor

If the focal length and/or crop factor for the camera-based perspective
correction tool are not edited, they will be set using the focal length
information found in the image metadata. This only applies to the editor
(batch editor and CLI still default to 24 for the focal length and 1 for
the crop factor).

rtgui/perspective.h

@@ -53,6 +53,9 @@ protected:
     Adjuster* projection_shift_vert;
     Adjuster* projection_yaw;
     LensGeomListener* lens_geom_listener;
+    const rtengine::FramesMetaData* metadata;
+
+    void setFocalLengthValue (const rtengine::procparams::ProcParams* pparams, const rtengine::FramesMetaData* metadata);
 
 public:
 
@@ -71,5 +74,6 @@ public:
     {
         lens_geom_listener = listener;
     }
+    void setMetadata (const rtengine::FramesMetaData* metadata);
     void trimValues          (rtengine::procparams::ProcParams* pp) override;
 };