Fix a bug generating the URL for CSV download
Fix a bug generating the URL for CSV download

Add a version parameter to the toString method on endpoints to generate
URLs correctly. This is used by the data explorer to generate the src
for the iframe used to download the CSV.

unicef/rhizome,unicef/rhizome,unicef/polio,unicef/rhizome,unicef/polio,unicef/rhizome,SeedScientific/polio,SeedScientific/polio,SeedScientific/polio,SeedScientific/polio,unicef/polio,SeedScientific/polio,unicef/polio