Save VFB Post and Lightmix config in the image metadata

Lightmix can be very useful when testing out various lighting and atmosphere scenarios on a rendered image. However, if there's a need to reproduce exact same lighting scenario on the image later on, one has to save both, post.conf and lightmix.conf somewhere alongside the image, and do this for each lighting scenario (so if Corona allows 10 Multiple Environment Maps setup, that means there's possible 10 (or more, if mixing different lighting together) post and lightmix configurations that would allow to reproduce desired results).

Solution - with each saved image file, save post and lightmix configuration files within the image file itself and allow to open it with VFB (or simply load configuration files from the image). These usually take up only a few bytes while the saved images are usually 10MB or more.