Upgrade the paperclip gem

* Converted test suite from test/unit to RSpec
* Refactored Paperclip::Attachment#assign
* Added Spanish and German locales
* Required Validators accept validator subclasses
* EXIF orientation checking can be turned off for performance
* Documentation updates
* Better #human_size method for AttachmentSizeValidators
* Allow MIME-types with dots in them
* Travis CI updates
* Validators can take multiple messages
* Per-style options for S3 storage
* Allow `nil` geometry strings
* Use `eager_load!`

https://trello.com/c/iZjRvOcl