Bugfixes for Locallab GUI

- Fixes segfault when modifying "Advice tooltips" option in Preferences
panel in "Multiple editor" mode
- Removes dedicated Locallab help button (will be managed directly in
RawPedia website)
- Fixes issue when switching to "Normal" mode with Retinex Locallab
tool.

rtgui/rtwindow.h

@@ -91,7 +91,6 @@ public:
     void on_mainNB_switch_page (Gtk::Widget* widget, guint page_num);
 
     void showRawPedia();
-    void showRawPedialoc();
     void showICCProfileCreator ();
     void showPreferences ();
     void on_realize () override;