Create the 'About content' widget

There should be an aboutcontent widget that has 2 different tabs. The first tab is the Details tab and shows the metadata of the content (title, description, url, created by). When a description is not available, it should not be shown. The second tab is the Shared with tab and shows the list of members of the content.
There's a problem with the download button in FF:

![screen shot 2014-07-10 at 18 22 40](https://cloud.githubusercontent.com/assets/109850/3542422/d515aa8a-0856-11e4-8ff5-0c71cbc06028.png)