Allignment view: rotating pages is slow

[nthiery]

Steps to reproduce:

1. Open the alignment view for a large exam; say https://correctexam.github.io/corrigeExamFront/imagealign/572
2. Click on the «rotate 180°» icon for one of the images

Symptoms: it takes ~45s for the image to be rotated, and in the meantime, all «rotate 180°» icons are hidden.

Use case: I inadvertently imported the copies 232-242 rotated head down. I don't see an easy way to reimport just them, so it seems I currently need to rotate the 100 pages by hand. Which would be ok if that was quick.

(In a perfect world, I would want to select a batch by drawing a rectangle, and run an action on all of them at once; but I see the point of CorrectExam not being there for supplementing better pdf management tools; it's just that, if you do a mistake, you are stuck).

Thanks in advance!