Add photos to batch upload

[hmchesner]

Background
Before you begin, please acquaint yourself with the project and the codebase.

Read about the project
Read the code of conduct
Read the contributing guidelines

Add photos to batch upload
Allow images to be uploaded in batch import - perhaps via the following:
Adding two columns in the csv: (1) with a url to a photo in Dropbox public folder (2) image label
(Would require updating the code to allow for this, the front-end batch upload page, and the wiki instructions for batch)