add TileWorker
use new link_to method in AssetGenerator
move CURRENT_PREFIX and IMPORT_PREFIX in S3
allow S3 upload to accept raw data, fix acl while moving files
call TileWorker during import
remove unneded opts from cover helper methods
remove unused AssetsController
Merge pull request #158 from unepwcmc/pregenerated-tiles

Pregenerated Mapbox tiles