Repurposing html() to be setter/getter and adding rawHtml() for plug-in ...

...development access. Deprecating xhtml() and _html()
[Radiant CMS radius tags](https://github.com/radiant/radiant/wiki/radius-tags).

I'm not sure what this test is trying to achieve but it is broken in master anyway and this change is theoretically not supposed to break it and it is a small change, anyway.