Use per-step protocol links from Vanderbilt

[mccalluc]

On the WG call today, I understood Jeff Spraggins to say that Vanderbilt will split up their protocols, so that each step has a URL on protocols.io. Once this has been done, vanderbilt-af/*-protocol.json should be updated to point at the right location.

(I believe this will just be for the data processing steps, not the tissue processing ones.)