#210 mathjax in .standalone files

[Lee Worden]

When we make .standalone.html, standalone.html5, and .standalone.xhtml files, we stick the MathJax script in them unconditionally, because at the time of making it, we don't know whether the people who view it will have the "no mathjax" preference set or not. Is it worth finding a way to sense it at the time of serving the file? It probably will be, if we end up using this as the default way to view latex files (in iframes).