Add links to GitHub history/blame pages

[thisisaaronland]

For example:

https://whosonfirst.mapzen.com/spelunker/id/85794639/

Should link to:

• https://github.com/whosonfirst-data/whosonfirst-data/commits/master/data/857/946/39/85794639.geojson
• https://github.com/whosonfirst-data/whosonfirst-data/blame/master/data/857/946/39/85794639.geojson