Fix tracking-vector image in dark mode

Since whatwg/whatwg.org@4aebf36 tracking-vector.svg is now dark mode-aware, i.e. its fill color will be dependent on the user's dark mode settings.

However, since whatwg/whatwg.org@dd2b988, <img> tags pointing at SVG images that don't have a "darkmode-aware" class are given a white background by default. This makes the tracking-vector image fully white when seen in dark mode.

Fix this by adding the class on generated <img> element.

src/wattsi.pas

@@ -1692,6 +1692,7 @@    TCrossReferences = record
                                               'alt', '(This is a tracking vector.)',
                                               'width', '46',
                                               'height', '64',
+                                              'class', 'darkmode-aware',
                                               'crossorigin', ''])]);
             (Node.ParentNode as TElement).ReplaceChild(TempElement, Node);
             Node.Free();