Photos are stored in the db rather than S3

[ti2ger92]

Photo uploads are typically stored in an S3 bucket and a url persisted to the database. We should refactor toward that approach for performance. This is low-priority at our scale, however.
The imageSrc attribute on a question record now stores a URL, so until we implement image-upload logic, edu team members can save images somewhere publicly accessible (TBD) and store the url with the image.
Original issue:

https://github.com/UPchieve/server/issues/30