make metadata updateable

[Jeltje]

Right now, if you make a mistake in your upload manifest.tsv, the only way to correct it is by redacting the file so it no longer appears on the File Browser, and then reupload the same file(s) with the corrected metadata.

In addition, Redwood makes assumptions based on the Donor UUID and other fields, and (for instance) adds files with the same Donor UUID to the same Project, even when the manifest tells it not to. This behavior is understandable but it should be possible to correct afterwards.