Add setting to disable HtmlLifter

[steveburchfield]

The HtmlLifter makes it very difficult to see differences in HTML responses in the UI. Since an HTML document can have a lot of nested elements, the amount of nesting in the differences map can be prohibitively large. Likewise, the differences view is cluttered with non-differences which makes it harder to see the real differences. It would be nice if there were a way to turn off the HtmlLifter and use string comparison instead via a setting.