LaTeX rendering for cell names

[jamievicary]

Hi Nick, thanks for implementing this cool feature! I have noticed a few issues:

• The font size between the code and rendered mathematics is different, and the edit box changes size as you mouse over it, which is visually distracting.
• I think it might be better to only replace the rendered mathematics with the underlying latex code when you click on the cell name edit box, rather than when the mouse hovers over it. Otherwise, as you move your mouse over the signature, you see lots of flickering as the cell names switch quickly between their code and rendered forms, which is distracting.
• It would be good to use this latex rendering for the tooltips when hovering over a cell in the main diagram.

[jamievicary]

Splitting into separate issues.