Sleuth File upload: allow unpublished studies

[jdkent]

Currently, the sleuth file upload requires an ID (PMID or DOI). If the user has an unpublished study we want them to be able to upload it.

[nicoalee]

Need to discuss: how are we handling this? We want to encourage the user to upload IDs whenever possible. How do we discourage lazy uploading while at the same time ensuring that it is possible to upload studies via sleuth if the study is unpublished (and does not have any pmid or DOI?)