Keep S3 concern.

We should be keeping s3 module that was removed by https://github.com/spree/spree/commit/b1d6c5e4b9801d888cc76c05116b814945122207#commitcomment-5389540 the settings are the same on every paperclip attachment.  Spree drops S3 support out of the box if this is removed.  This allows you to set them in an initializer and share them with Spree & it's extensions.

/cc @cbrunsdon @sworbel