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.
The Download button still has a display issue in FF 30.0:

![screen shot 2014-07-18 at 12 20 40](https://cloud.githubusercontent.com/assets/109850/3625535/9459ee94-0e6d-11e4-9d2b-0ed95bfc49f9.png)