[Suggestion] Thumbnail can be generated by the size we set

[sychn]

Hello,

The thumbnail size setup function of the screenshots is too weak in Downloads of current version. It would be much better if we could set the dimensions or the file size of the thumbnail and let the system to do the scaling job. If I uploaded a 5MB picture as a screenshot, then it would show up as the original size which is very slow sometimes.

Thanks.