Create multiple, smaller zip files to avoid timeout errors

[ngreenwald]

Is your feature request related to a problem? Please describe.
As described in vanvalenlab/kiosk-client#59, there is currently an issue with zip uploads which are too large (somewhere around 150 Mb). It's a bit of mystery why this is happening.

Describe the solution you'd like
It would be good for us to figure out about how many 1024x1024 images we can safely upload without running into this error. We'll first need to address #301. Once we know what that number is, we can decide what our next steps are. We can either wait until the bug gets fixed in the kiosk, or add functionality to create multiple, smaller zip files, each of which gets uploaded separately, to work around the issue.

[ngreenwald]

Okay, looks like this issue is popping up again. Putting this back in the queue to get worked on