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.
No need to do `oae.api.util.security().encodeForHTMLAttribute` here. I'll follow up