rsc_attachment_formatter

Adds formatters for attachment fields.

What it does:

Defines four field formatters

• List of links
• Download (sends a force-download header)
• Open (a direct link to the file)
• Google Drive (open the document via http://docs.google.com/viewer?url=…)
• Direct link, with JS dropdown
• Same as above, but only the direct link is visible. Other links are hidden in a drop-down or pop-up list (depending on how CSS is applied).
• HTML5 audio element & download link
• Automatically choose a formatter based on the mime type (works for text, video and audio)

TODO: video formatter (probably allow embedding from Youtube)