Display list of files already attached to the submission

[htpvu]

• Highlight flagged files
• Allow user to upload new version of each file
• Allow user to edit the user-entered file metadata?
• Allow user to remove a file from the submission

[jabrah]

Part of Files step initialization, #21, #15 with some additions

• Make sure that users can upload a new version of a file with the Edit button
  • Relies on OneDrive file picker integration