External linked content cards

- New: timestamp
- New: on external links, display the provenance (domain) at the bottom of the card
- New if switched on: cardify external links to wikipedia, youtube, BBC, vimeo, dailymotion, gov.uk

![screen shot 2013-08-27 at 12 59 52](https://f.cloud.github.com/assets/85783/1034145/7eb9dc8c-0f10-11e3-806f-a48b3a7a41d9.PNG)

![screen shot 2013-08-27 at 12 59 42](https://f.cloud.github.com/assets/85783/1034146/816f81fc-0f10-11e3-8060-a92a8d401946.PNG)

Big thank you to Darren, Dai, and Patrick, as well as Matt for inspiration.

![erk](http://s1.developerslife.ru/public/images/gifs/4bbcdc41-5539-4071-88ef-015683d0cddb.gif)