Add mathjax js in Email notification

[vanabel]

In the digest email, it write

A brief summary of MaCuz since we last saw you on xx-xx-2014.
...

If the content contains many math formula, then it is better to render it by mathjax, how do you think?

[lidel]

I think even if you include JS library in HTML of an email it will be filtered out by email client as a security measure.
So to make this work, it would require TeX to be rendered on the backend before email is sent.

[nouiz]

I think it is still not implemented. We would also like to have this done. So +1 :)

thanks for the good plugin.