The code for this task will be derived from branch MMDB-1668-update-dataset-file-uploader, from task MMDB-1668.

It relies on the work done there. The work for this task will be to design the interface so that existing datasets can have multiple files added to them either a) as part of uploading multiple new files or b) allowing a user to select multiple existing files and attaching them to the dataset.

The goal is to streamline and make more accessible the ways that users can add files to datasets.