File exchange service needed

This is to track a feature needed following separate discussions with cloomis and Neven Caplar: it is often needed for development purposes to exchange FITS files, images and other data files between different groups. Currently dropbox and GitHub have been used for this end, but a more formal means should be investigated.

For example, a simple file server (SFTP?) hosted by Princeton that addresses data sent in/out of PU is one possibility. A more centralized server for PFS is ideal, but it is not clear if this is possible. GitHub-LFS needs to be investigated.