[ProPublica.org] add map tile CDN

As used in [this project](http://projects.propublica.org/louisiana/) and some other places that don’t have protocol scheme smarts just yet.

i.e.
http://tiles-a.propublica.org/louisiana/raster/1/505/847/11/processed_loss_gain_0.png
ꜜ
https://d3i4wq2ul46tvd.cloudfront.net/louisiana/raster/1/505/847/11/processed_loss_gain_0.png