Currently there's a nasty blink when revealing the answer if the answer
has images on it, as the entire card is hidden, and not shown again until
the images have loaded. This patch removes the wait, so text should appear
more quickly, but it will mean the images may pop in.
We still wait for images before scrolling, to avoid a scroll to the wrong
location.
There's plenty of scope to improve this further - preloading images,
rendering MathJax in advance, etc, but those changes will need to wait
for now. #1120 has some related discussion.
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