Use `texvcjs` package to validate/translate math markup.

Change-Id: Ibeaaa85cd20aea444d905b263503e3af19329855
Skip math content if `teubner`, `cancel`, or `euro` packages are required.

We don't include these packages presently.

Change-Id: Ic704b063100d7d1cd2b0287ed389137a412bba18
Latexer should not die on a bad image

Sometimes the conversions fail because the images are corrupted. Catch
the error, report it, and continue on.

Change-Id: Icc82743671f6c4e2dfb06695d2a882eb05391e04
Merge "Skip math content if `teubner`, `cancel`, or `euro` packages are required."
Use `jpegtran` to purge EXIF data from jpegs.

XeLaTeX will still give images the wrong size when there is certain EXIF
information attached to the JPEG.  Use the `jpegtran` utility to clean
EXIF information from the JPEG before we give it to XeLaTeX.

Change-Id: I1c00dc80ff052d71371300c10b16d86e98fb02ab