Updates to LaTeX code.

These commits pick up a few changes that were made on Anki for handling LaTeX.

Mainly, this causes the hash used to generate the name of the LaTeX cached image to change, making AnkDroid incompatible with Anki desktop. This might cause issues for users of AnkiDroid that have an outdate version of the desktop app, but we can assume everyone will be updating their app and we cannot (easily) be compatible with both.