Consider implementing better RAW processing method

[Xevion]

As of now, processing RAW files literally deletes my system's RAM and will crash computers it's so slow, this is due to the insanely out of control multiprocessing threads implementation.

I think it's due time for a better implementation. One optimization would be thumbnails: extracting a full size JPEG from the RAW file, and then extracting a tiny thumbnail from that yields a large IO processing time that NEEDS to be cut down if full library processing is going to be anywhere near feasible.

preview-generator may yield a good results, but due to it being a rather new module, we should leave open options for multiple possible processing methods in the commandline options.

Perhaps looking into external image processing programs would be a good idea, including them as different 'thumbnail methods'.