Re-add inspector tab as an option (#5867)

- add option "inspectorWindow" to switch from tab to fullscreen view
- add option "zoomOnScroll" to configure scroll device for zoom or pan
- add both options to preferences
- filepanel creates tab if not inspectorWindow
- inspector adapts to settings inspectorWindow and zoomOnScroll
- filebrowser shows context menu item for inspector only if inspectorWindow

rtgui/inspector.h

@@ -54,13 +54,14 @@ private:
     bool active;
     bool pinned;
     bool dirty;
+    bool initialized;
     bool fullscreen;  // window is shown in fullscreen mode
 
     sigc::connection delayconn;
     Glib::ustring next_image_path;
     rtengine::Coord2D next_image_pos;
 
-    Gtk::Window window;
+    Gtk::Window *window;
     bool on_key_release(GdkEventKey *event);
     bool on_key_press(GdkEventKey *event);