Add @fred-wang CSS for MathML fallback

The CSS was based on
https://github.com/fred-wang/mathml.css.

This should close bug 981409.

Thanks to @darkwing for the help.

- Add CSS MathML fallback
- Add Javascript to test for web browser MathML support
- Add Javascript to add warning when browser not support MathML

TODO:

- Localization for warning.
Remove function call

as suggest by @darkwing.
Merge pull request #2196 from r-gaia-cs/bug-981409

Add CSS for MathML fallback