[export v2] use node-data to extract vaccine information 
[export v2] use node-data to extract vaccine information 

This closes #407. By allowing vaccine info to be set via the node-data JSONs we facilitate a clear mapping between provided data & exported data, and treat this as an independent input rather than a part of the "auspice config". In the future, a node-data JSON schema should validate this input.
nextstrain/augur,blab/nextstrain-augur,nextstrain/augur,nextstrain/augur