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/preferences.h

@@ -148,6 +148,9 @@ class Preferences final :
 
     Gtk::ComboBoxText* complexitylocal;
 
+    Gtk::CheckButton* inspectorWindowCB;
+    Gtk::CheckButton* zoomOnScrollCB;
+
     Gtk::ComboBoxText* themeCBT;
     Gtk::FontButton* mainFontFB;
     Gtk::FontButton* colorPickerFontFB;