Use image thumbnails instead of displaying the full image

[mayeaux]

Currently when an image is uploaded that raw image is used as its thumbnail on places like the recent/popular media pages and the channel overview page.

Ideally to reduce bandwidth usage of users and increase page load time we'd want to have compressed version of those images used for thumbnails.

Note: .gif files should stay dynamic though I don't want those turned into a still image.

[mayeaux]

Also I should note that I'm a little iffy about adding an installation step (ImageMagick) for such a small use case, so this feature should probably be behind a flag so people don't have to install ImageMagick to boot their NodeTube instance