Allow dots in s3 bucket name and allow custom CDN path

CDN path can be used if user is using CloudFlare and uses S3 as virtual host https://support.cloudflare.com/hc/en-us/articles/200168926-How-do-I-use-CloudFlare-with-Amazon-s-S3-Service-

Previously dot is not allowed in s3 bucket name due to ssl constraint, changing the position to `https://s3.amazonaws.com/' + config.bucket + '/';` fixes it