Add a new 15 FPS publish option for timelapse videos

[tom95521]

I have been experimenting with timelapse by combing images with short slide duration. By adding a very short dissolve transition between slides it appears to smooth the video (often called blending in other timelapse software). Motion blur does not seem to make a difference. If we had a 15 FPS publish option then the file size would be smaller (depending on movement between frames). Also if slide chapter markers could be added to a video it would make comparison easier.

Thanks,
Tom