(bug 3112) Adding colors for active and visited external links.

(bug 3112) Adding colors for active and visited external links.
This is in-core for internal links and red links, but there's no visual clue of active and visited links for external links.

Normal external: #36b;
/* Added: */
Active external: #b63;
Visited external: #636;

These two colors (orange and purple -ish) are in the same saturation/brightness as the blue for normal (inactive/unvisited) external links.
Since these visual clues were also lacking in external links to interwikis I've replaced that override with similar colors as well.