Remove 'save on exit' feature for now

[michaelwschultz]

There is no way I'm going to be able to add this before 1.0. Might as well remove the feature for now.

[michaelwschultz]

Thinking about it more. This may be possible. When saving each photo, we should also update a session file that includes the current state object. This file could then be dropped back into the window to reconstruct the current state.

timelapse: {
  created_at: 'Fri Oct 25 2019 00:00:00 GMT-0700 (Pacific Daylight Time)',
  directory: 'timelapse-2019-10-25-12389',
  photos: [
    'timelapse-photo-1.png',
    'timelapse-photo-2.png',
    'timelapse-photo-3.png',
  ],
  session: {
    last_photo_taken_at: 'Fri Oct 25 2019 00:00:00 GMT-0700 (Pacific Daylight Time)',
    photo_frequency: '5 seconds',
    photos_taken: 3,
    photos_to_be_taken: 720,
    photos_until_finished: 717,
    timelapse_length: '1 hour',
  },
}