Dataset cards / Better support for embed.ly

It would be nice to have dataset cards which are a small embeddable rendering of the key information for the dataset, similar in concept to twitter cards ( https://dev.twitter.com/docs/cards )

This may also allow a better source for embed.ly, which by default does a reasonable job of pulling content from CKAN*. I expect it might be nice if I had a template I could customise within CKAN and use have embed.ly/dataset-cards use that.
- go to embed.ly and paste in http://data.gov.uk/dataset/index-of-multiple-deprivation for instance.

Start with the linked Twitter Cards reference and test the data.gov.uk dataset URL in embed.ly, as described in the issue. Define the dataset-card content, customization boundary, and embed.ly behavior before locating implementation work; the issue names no files or tests, so completion criteria remain to be specified.

Written by the indexing model from the issue text.