Created the 'html' addon for QUnit: `htmlEqual` & `notHtmlEqual` assertions

Created the 'html' addon for QUnit, introducing `htmlEqual` and `notHtmlEqual` assertions.

This is a throwback to the `assertHTMLEquals` method from very-deprecated [JsUnit](https://github.com/pivotal/jsunit), which compares two HTML strings after doing some normalization.  My implementation takes it a step further by also sorting the attribute nodes before doing the final comparison since modern browsers do not predictably sort the attributes like the old browsers usually did.