Keep S3 concern.

We should be keeping s3 module that was removed by https://github.com/spree/spree/commit/b1d6c5e4b9801d888cc76c05116b814945122207 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