[#58772462] added 'add attachement' feature and attachment button images
[#58772462] added attachments controller and starting making specs pass
[#58772462] added attachment model
deleted unnecessary files
added AttachmentsController#create implementation
[#58772462] finished AttachmentsController#create implementation
removed debug code
[#58772462] finished attachments controller implementation
[#58772462] finished making the 'add attachment' feature pass
[#58772462] added content for the attachments
[#64469126] added 'view attachment' feature and made it pass
added 'delete attachment' feature and made it pass
[#64680394] added attachment view model and started to implement attachment behaviors
updated gems
set transparency on attachment images
[#64680394] added style class for small attachment buttons
updated erd diagram with attachments
[#64680394] added initial javascript implementation to show an attachment
[#64680394] inverted the relationship between attachment and attachment_content
[#64680394] wired up the 'show attachment' button