Attachments now download vs. view

* Adds method download_url to attachment
* http://stackoverflow.com/questions/12939903/allowing-user-to-download-file-from-s3-storage#answer-16426114
Clean up whitespace and hash syntax
Clean up whitespace and hash syntax
Merge pull request #307 from ophrescue/issue/attachments-show-not-download

Issue/attachments show not download