This sub-issue is required to completed #25.

See the "reload image mechanism" section in this comment from #25 for information about this issue.

In my source code I've littered TODO comments everywhere for the reload image mech:

• TODO: https://github.com/cloudy-org/roseate/blob/feat/dynamic-downsampling/src/image_handler/mod.rs#L134
• TODO: https://github.com/cloudy-org/roseate/blob/feat/dynamic-downsampling/src/image_handler/mod.rs#L198
• reload method that needs to be implemented: https://github.com/cloudy-org/roseate/blob/feat/dynamic-downsampling/src/image/image.rs#L120-L142
• image.reload_image should decide whether it should load from file or memory.
• Always call image.reload_image in image handler's .update() method.

Also #57 will probably significantly help this implementation, so I think this issue may need to wait until the Image.image_pixels array stuff is implemented via #57 so we can skip on re-encoding to image bytes and have a chance to simplify this implementation.