Uses CDN for S3 downloads
Updates tests
Fixes download mailer test
Don't show clear filterse link in search if there are no filters
Merge branch 'frontend-do-over' into s3-cdn

* frontend-do-over:
  Don't show clear filterse link in search if there are no filters
Use correct method to retrieve PA cover image
Forgot about those pesky envs
Moves PA tile retina styling to CSS

The asset tile generator no longer supports custom sizes
Merge pull request #159 from unepwcmc/s3-cdn

Uses CDN for S3 downloads
select fields for countries in search for performance reasons
Merge branch 'frontend-do-over' of github.com:unepwcmc/ProtectedPlanet into frontend-do-over
use country placeholder for pa with no mapbox tile
Merge branch 'frontend-do-over' into country-page-optimisations