Add ko.utils.setHtml to KnockoutUtils interface (2 overloads total).

I needed this to author a custom knockout bindingHandler in TypeScript. The bindingHandler invokes ko.utils.setHtml(element, valueAccessor()), similar to how knockout's internal html bindingHandler invokes the same utility function.

Relevant knockout source code:

    ko.utils.setHtml = function(node, html) {
        ko.utils.emptyDomNode(node);

        // There's no legitimate reason to display a stringified observable without unwrapping it, so we'll unwrap it
        html = ko.utils.unwrapObservable(html);

        if ((html !== null) && (html !== undefined)) {
            if (typeof html != 'string')
                html = html.toString();

            // jQuery contains a lot of sophisticated code to parse arbitrary HTML fragments,
            // for example <tr> elements which are not normally allowed to exist on their own.
            // If you've referenced jQuery we'll use that rather than duplicating its code.
            if (typeof jQuery != 'undefined') {
                jQuery(node)['html'](html);
            } else {
                // ... otherwise, use KO's own parsing logic.
                var parsedNodes = ko.utils.parseHtmlFragment(html);
                for (var i = 0; i < parsedNodes.length; i++)
                    node.appendChild(parsedNodes[i]);
            }
        }
    };