Made it so you can press END or i to ignore boxes in imglab. I did this

because it's a much less stressing hand motion to hit END that i in most cases.

dlib/gui_widgets/widgets.cpp

@@ -6440,7 +6440,8 @@ namespace dlib
                 event_handler();
         }
 
-        if (is_printable && !hidden && enabled && rect_is_selected && (key == 'i'))
+        if (!hidden && enabled && rect_is_selected && 
+            ((is_printable && key == 'i') || (!is_printable && key==base_window::KEY_END)))
         {
             overlay_rects[selected_rect].crossed_out = !overlay_rects[selected_rect].crossed_out;
             parent.invalidate_rectangle(rect);

tools/imglab/src/metadata_editor.cpp

@@ -625,7 +625,7 @@ display_about(
                         "field at the top of the application.  You can quickly edit the contents of the Next Label field "
                         "by hitting the tab key. Double clicking "
                         "a rectangle selects it and the delete key removes it.  You can also mark "
-                        "a rectangle as ignored by hitting the i key when it is selected.  Ignored "
+                        "a rectangle as ignored by hitting the i or END keys when it is selected.  Ignored "
                         "rectangles are visually displayed with an X through them.  You can remove an image "
                         "entirely by selecting it in the list on the left and pressing alt+d."
                         ,0,0) << endl << endl;