Use htmlDiff for webDiffer

[kakwok]

difflib.htmlDiff provides considerably more readable diff tables than line-by-line diff.
webDiffer could use this method so that user will get a nice displace when re-directed from the bot message.
Here's short snippet of example usage:

  htmlDiffer = difflib.HtmlDiff(wrapcolumn=90)
  body = htmlDiffer.make_table(earlierCfgScript, laterCfgScript, "", "", True)