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
Merge "Breakdown of texvc"