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.
I still don't think we need the modal-footer here. However, because the items in `oae-list` are floating, you do need to add `clearfix` to `modal-body`. After doing that, the padding is fixed and there's no further need for this footer element.