Table-driven construction of Prefs dialog. A factory for each kind of panel...

... and maybe a future plug-in protocol to break compilation dependency on
all of the PrefsPanel subclasses.

src/prefs/ImportExportPrefs.cpp

@@ -109,3 +109,8 @@ bool ImportExportPrefs::Apply()
 
    return true;
 }
+
+PrefsPanel *ImportExportPrefsFactory::Create(wxWindow *parent)
+{
+   return new ImportExportPrefs(parent);
+}