Breakdown of texvc

texvc had several tasks in the past:

1 checking the input
2 convert MediaWiki custom syntax to standard LaTeX
3 run LaTeX
4 convert dvi2png

This change provides a simplified version that performs
only steps 1+2. This is required to avoid security problems
with tools like MathJax, especially if these tools are
run at the server-side.

Bug: 54624
Change-Id: I1650e6ec2ccefff6335fbc36bbe8ca8f59db0faa
Math 2.0

* MathML support with SVG fallback
* Distinction between inline and display-style
* MathJax now available independent of the rendering mode
* Debug functionality
* independent of the file-system
* backwards compatible, without dependencies to it
* removes dependencies to math specific core functions
** getMathOptions()
** armourMath
* Asynchronous generation of Math images
* upgrade to MathJax 2.3, use the unpacked version and remove unusued files
* use MediaWiki's resource loader for Javascript files
* improve the way MathJax is configured
* make math fonts available as Web fonts for native MathML
* The MathML/SVG output is used as a preview while MathJax is processing

MathML is currently displayed for Firefox and MathPlayer users only.
By default it is wrapped in a hidden span or div element.

SVG generation is done by using MathJax on the server-side.

(See a live demo http://math-test2.instance-proxy.wmflabs.org/wiki/Fourier_series)

PS31: Adresses the displaystyle concern of Frédéric (http://math-test2.instance-proxy.wmflabs.org/wiki/Displaystyle)
and the ID feature request of Gabriel Wicke (http://math-test2.instance-proxy.wmflabs.org/wiki/IDs#eq.20-sim)

PS35: Add extra cache keys.

PS49: Edit merge conflicts with I9066f6b2606044412a9b91ca395e841550d7e787

Change-Id: I5132901ed2072c6af7b9ed82d267200d64c67939