commentaries: replace <img> tags with dtext links (#3586)

Replace <img> tags with dtext links, unless the <img> tag is already
inside an <a> tag.

Also strip Unicode spaces from DeviantArt commentaries.

app/logical/sources/strategies/deviant_art.rb

@@ -52,7 +52,7 @@ module Sources
               element["href"] = uri.to_s
             end
           end
-        end
+        end.gsub(/\A[[:space:]]+|[[:space:]]+\z/, "")
       end
 
     protected