change s3 resource url from path-style to domain-style

S3 EU buckets need to be referenced with the bucket name in the subdomain (US buckets can be access both ways).

Also, with the EU region, the 's3.buckets.create' method will not find existing buckets. This pull request first checks for an existing bucket before creating one.
Why? Is there currently a problem with font-awesome?

This has to be changed somehow. In sharetribe.com we have a couple hundred marketplaces that use custom styles and those custom css files have to go to a subfolder. The `assets/` folder is already messy enough :)