S3 cache: regular tiles and layers are put in different locations

[hampelm]

We're putting regular tiles in $S3_BUCKET/$NAME/$surveyID but cached layer tiles in $S3_BUCKET/$NAME/surveys/$surveyID.

Eg:

https://localdata-tiles.s3.amazonaws.com/production-tiles/surveys/fb6dbc30-7bd9-11e4-abaf-a39ffd5c50e6/layers/0adcbf0ffe34b2d0fc283a46331395a5491b3487/tiles/18/72882/98804.png

vs

https://localdata-tiles.s3.amazonaws.com/production-tiles/9d3ced80-6cc1-11e2-be36-692120106a91/tiles/18/70600/96988.png

We should standardize on one or the other for easier cache clearing.

[prashtx]

The cached tile locations are based on the original URL. I'd support modifying the legacy tile URL for consistency, but we'll need to change the dashboard to match.