Provide image scaling via GET parameter

[stefan-niedermann]

Attached images should be scalable via a parameter to reduce the size for previews.

Similar to the avatar endpoint one could add something like

https://<image-uri>/64

for a scaled down version of the image which fits into a 64x64 px square.

Alternatively a GET parameter like

https://<image-url>?size=64

would work, too.

Would also be needed for #1635 (comment) but since we have an Android client in the meantime, this might be even more important 😉

[juliusknorr]

Makes sense 👍

[stefan-niedermann]

We have to decide whether or not the image should be cropped.

Avatars are always quadratical, which makes it easy, but i guess most attached images are in formats like 4:3 or so because they are photos.

Since my intention is to use it as previews, i would prefer to first center-crop them before downscaling, otherwise the preview thumbnail grid will look a bit messy.

What do you think?

[juliusknorr]

Once we have #2638 the files preview api can handle all of that, so let's close this here.