Handle in SI and other files

[markwhiting]

Automatically attempt togged SI, registrations and any other linked content from a paper.

We should also be able to add these manually to a paper's record.

[markwhiting]

Probably set this up as an agent that looks for things like "SI appendix" or "aspredicted" or "osf" etc. and then downloads the content. Probably if we think this is available we should not process features until we have the documents.

Might be nice to also look at code and data if they are available.

Features should be able to look at all files.