Upgrade Paperclip 4x to 5x

Paperclip is now compatible with aws-sdk >= 2.0.0.

If you are using S3 storage, aws-sdk >= 2.0.0 requires you to make a few small changes:

• You must set the s3_region
• If you are explicitly setting permissions anywhere, such as in an initializer, note that the format of the permissions changed from using an underscore to using a hyphen. For example, :public_read needs to be changed to public-read.

For a walkthrough of upgrading from 4 to 5 and aws-sdk >= 2.0.0, watch http://rubythursday.com/episodes/ruby-snack-27-upgrade-paperclip-and-aws-sdk-in-prep-for-rails-5

For those using Paperclip with :s3_server_side_encryption: Note that AWS no longer accepts :aes256 as an encryption value and will raise Aws::S3::Errors::InvalidArgument with the message The encryption method specified is not supported. The value should instead be "AES256".