New feature: Segment videos by max file size

[ChristopheVeber]

Background

As an contributor, I typically try to upload GoPro timelapse videos.
As videos get larger the risk increases that the data ingestioon never completes and any kind of time-out or other hickup occurs.
For example, the Android app cuts recordings into segments of max 300 images which seems to be a value on the safe side for Mapillary processing.

New Feature Proposal

By default, videos uploaded should be split into multiple lengths so that the individual segments are on the safe side for processing.
As an optional commandline argument, a deviating segment length (expressed either in time or number of images could be provided