Optimization of work with cache

[user100]

- Add the ability to create a cache of images in the folder where the images themselves are located. If the mode of creating cache of images in a folder was later changed in the program settings to the general cache and there are no thumbnails in the general cache, then check if there is a cache in the folder (or vice versa, as faster for the application).

- Add the ability to check for non-existent images from a specific image folder, not just all folders at once, from the settings.

- When moving/copying images with xnview, from one folder to another, also copy their thumbnails in the cache, so you don't have to re-create them in a new folder (where you moved/scoped them to).

- When renaming files in a folder using xnview, do not recreate thumbnails for the same files with a new name, but also rename them in the cache so that no waste and unnecessary work has to be done.