Import additional open datasets

[missinglink]

Create mapping scripts for other interesting open data providers:

• US Census ZCTA Tabulation Areas
• OpenAddresses
• Geonames
• GB postcode data used in nominatim (listed at the bottom of the page)
• Ordnance Survey Open Data
• Swiss Open Geo Data
• UK Postcodes (point-only)
• Statistics Canada (note selecting a census year yeilds more download optons) ... etc

Please comment to suggest additional data providers.