Streamline the folder addition routine to allow group selecting directories to add, and accepting subdirectories. Tune the image loading so it takes less time.

Having to click on the "add" button and work through the add directory dialog is onerous. It would work better if user could group select directories and include (or exclude) sub-directories for addition. It also seems to be a waste of resoources to load all 1500-5000 files before starting the generation. Most computers can't hold that many images in memory, so why do it. Make a quick and efficient parse that quickly loads the average intensity of the image (or whatever property is of interest).