feat(frame-grab.js) functional make_story method  #2

TODO:
- Come up with better algorithm for determining time for each frame.  Currently, if the user asks for 2 images to be generated, and the video is 1 minute long, the first image is generated at time 0, and the second at the 30 second mark.  A better story would include a frame from the 15 second mark, and perhaps another from the 45 second mark.