Add AttachmentToHTML::Adapters::GoogleDocsViewer
Add AttachmentToHTML::Adapters::CouldNotConvert

Fallback adapter to display something useful in the event that an
attachment can't be converted by anything else.
Fall back to GoogleDocsViewer or CouldNotConvert

When an FoiAttachment can't be converted or fails to convert, fall back
to a GoogleDocsViewer or CouldNotConvert
Cache AttachmentToHTML::Adapters #title

Stops executing SQL every time we call #title