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.cc

@@ -127,3 +127,9 @@ void MetaDataPanel::metaDataModeChanged()
         listener->panelChanged(EvMetaDataMode, M("HISTORY_CHANGED"));
     }
 }
+
+
+void MetaDataPanel::setProgressListener(rtengine::ProgressListener *pl)
+{
+    exifpanel->setProgressListener(pl);
+}