Support all symbols with unescapeHTML

The `unescapeHTML` utility is very explicit about what it unescapes and does not handle more than the 5 basic HTML symbols we have defined in the escape map.  

I don't believe managing a full map is a good idea, so I'm relying on the browser to unescape the text and returning that. `escapeHTML` is still more worried about just escaping the basic HTML characters so I've left it using the original escape map. 

The test ensures at least one character from each category defined in the spec (http://www.w3.org/TR/html4/sgml/entities.html) is supported

@cjoudrey @nciagra please review