Improvements to prepare a MathJax+PNG option

- Remove MathMathJax.php, which uses exactly the same output as MathSource.php.
- Make wiki2jax able to handle texvc output as a preview before MathJax rendering.

Change-Id: I1199cb34d555d2a1e57da98857f41a22cfe81df4
Merge "Improvements to prepare a MathJax+PNG option"