Free allocated exp settings.

Code to properly free exp settings when we rebuild the modifer list.

1) Fix up mislabeled modifier settings for Presence.

2) Add missing xml settings (avoids crashes with -D a).

3) When we free the modifier group, free the data associated with the
   dynamically allocated settings for the EXP_POSITION combo box.

gui.h

@@ -31,5 +31,6 @@ gboolean unsupported_device_dialog(Device **device);
 gint select_device_dialog (GList *devices);
 const gchar* get_message_name(MessageID msgid);
 void create_modifier_group (guint pos, guint id);
+void modifier_settings_exp_free(EffectSettings *settings);
 
 #endif /* GDIGI_GUI_H */