LaTeX blinking

[edemaine]

When changing a LaTeX formula, the old one blinks away while the new one gets rendered. Ideally we could display the previously rendered formula, or a text version of the formula, while we're waiting for the renderer. I'm not sure how easy this is to do (in particular, how do we maintain a bijection between old and new?), but it'd definitely be a nice UX improvement.

(Suggested by Yevhenii.)