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.
After discussion with design, this should be renamed back to `About`. That probably means the widget needs to be renamed back to `aboutcontent`. Sorry for this :sob: