Add Paperclip

Hi Trung

I have installed Paperclip to add an attachment, but I have a few issues

1. This required a new column called 'attachment' to be added to my Item model when I already have an attachment model in my plan. How is this new column in Item related to my Attachment table in my database schema?

2. I couldn't do styles on it yet, I kept getting the following error 

An error was received while processing: #<Paperclip::Errors::NotIdentifiedByImageMagickError: Paperclip::Errors::NotIdentifiedByImageMagickError>

I have tried a number of things, but no luck yet. Will keep Googling.

3. So, we created this to upload code files for a theme - is that correct? so I need to change this to accept html and css files?
remove the `self`, just `def down` or `def up`