metadata: allow the user to specify XResolution/YResolution

see https://discuss.pixls.us/t/note-to-the-dev-guys-about-72-ppi-output

(cherry picked from commit ad237944699800368ba50151f6774ee203d61ed5)

rtgui/metadatapanel.h

@@ -45,5 +45,7 @@ public:
 
     void setImageData(const rtengine::FramesMetaData* id);
     void setListener(ToolPanelListener *tpl) override;
+
+    void setProgressListener(rtengine::ProgressListener *pl);
 };