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/exifpanel.h

@@ -99,6 +99,8 @@ private:
     std::unordered_set<std::string> initial_active_keys_;
     std::unordered_set<std::string> cur_active_keys_;
 
+    rtengine::ProgressListener *pl_;
+
     void addTag(const std::string &key, const std::pair<Glib::ustring, Glib::ustring> &label, const Glib::ustring &value, bool editable, bool edited);
     void refreshTags();
     void resetIt(const Gtk::TreeModel::const_iterator& iter);
@@ -136,4 +138,5 @@ public:
 
     void notifyListener();
 
+    void setProgressListener(rtengine::ProgressListener *pl);
 };