[Enhancement] Add thumbnail cache option

[do-i]

It will be nice to have thumbnail cache option.
If you select cache option, images that are visited once cached as thumbnail size. Subsequent visit to the same images will use the cached (smaller size) will be loaded in thumbnail view.

[vnaum]

I second this.

[FreeSlave]

Just remember there's a freedesktop spec for this task (to share thumbnails with other apps).
There's also a thumbnail cache for Windows Explorer, but I'm not sure if it should be used by third-party applications.

[sandsmark]

Unfortunately the freedesktop spec is unmaintained and not very suitable for "modern" systems (with bigger displays and higher DPI. The absolute maximum for normal thumbnails is 128x128 and "large" thumbnails must be exactly 256x256 (which is both too small for my displays, at least, and means that anything between 128x128 and 256x256 needs to be rescaled every time).