File management update

Added threading to process file movements separately from main program.
Look for NEF EXIF if JPG lookup fails

If EXIF data is missing from a jpg then it looks for the NEF if it
exists and copies the data to the new JPG
Method added to output JPG from NEF

Adds the option to save the preview full-size jpg from a NEF file as a
separate image. Corrects orientation and copies NEF EXIF to JPG.
Now preloads and stores recent image data

Preloads next few files and speeds up displaying of images.
Uses thread module to preload. Adds option to output JPG from NEF and
delete NEF.