Create the 'About discussion' widget

There should be an aboutdiscussion widget that has 2 different tabs. The first tab is the Details tab and shows the metadata of the discussion (title, description, 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 discussion.
I removed this from the `aboutcontent` widget to fix a margin issue when there was only 1 item. Can you make the same change and move the associated CSS rules over as well?