buttons linking directly to downloadable OSF and Zenodo dataset versions in CONP portal

Our links to OSF in the CONP portal currently point at the overview pages for each dataset: `https://osf.io//overview`

OSF are fine with us linking directly to the archived zip files for each dataset, at the address
`https://files.us.osf.io/v1/resources/znt9d/providers/osfstorage/?zip=`, which has worked fine in my tests and could be automatically generated.

Zenodo are also good with direct links to their data, and links to the relevant files are stored in the `files->links->self` entry in the response to an API call to ` https://zenodo.org/api/records/`. In this case the structure of the link is more complex and does not look to be automatically derivable from `` so we would need to retrieve this for every Zenodo dataset.

If we proceed with using these values as the default download links for OSF and Zenodo datasets in the CONP Portal interface, do we still want to store the overview page links in DATS.json as well? It seems to me that the options here are a) replace all the existing links, or b) add a new field storing the zip file download link (or dragoon some other part of the existing DATS format into that purpose).