Thumbnail generation and large folder loading could be faster in general

## Problem

Thumbnail generation and large folder loading could be faster in general.

## Proposal

As of this writing, Elementary OS generates image thumbnails faster than the default file managers in other distros, but the wish is to load large folders instantaneously, or at the least, fast enough that the user does not notice the wait. This will be useful for artists and those who manage thousands of images in a folder and would rather not wait several seconds or minutes for a large folder to load, and do not want to install another file manager because Files is great!

The image thumbnailer and/or whatever loads the files could utilize multiple threads and/or the GPU. Currently, it appears that Files does most, if not all, of its processing on only one CPU thread. Most users these days have multi-core, multi-threaded processors and powerful GPUs.

If whatever code that currently loads the files is based on ancient code/libraries, then that code could be rewritten to take advantage of modern hardware.

## Prior Art