Improve the ability to enter multiple metadata values quickly.

As an end-user of Clowder, I would like to be able to add multiple metadata fields at once on a File. This would allow me to add metadata to files much more quickly.

Currently users must add these fields one by one, which makes the process of adding many metadata fields very tedious and slow. This could be improved for Advanced users by listing off all possible Metadata fields and allowing them to fill-in whichever ones they want to populate.

We can maintain the existing single-field functionality under an additional option for Basic users.

This ticket is complete when Clowder's File View allows users to attach metadata fields in bulk.