Increasing performance of image load times

[galpt]

I'm opening this so anyone can discuss about improving image load times for potentially any manga websites as long as the image is cache-able.

Refer to #771 for more information.

This suggestion will:

1. Make image load times more predictable for most users;
2. Give users the ability to compare it to wsrv.nl;
3. Reducing server load for the manga websites when users want to download certain manga chapters.

The code implementation should be quite simple since the logic is only about adding a prefix (i.e. https://0ms.dev/mirrors/) to the manga image URLs.

When users want to download certain manga chapters, instead of downloading from the original image URLs, Kotatsu app should download the images from the caching proxy URL, so multiple downloads of the same manga chapters won't end up being slow or burdening the manga websites, at least for the next 24 hours.