Epic work item type added in Visual Studio Online

We updated our three out-of-the-box process templates to include new fields and a new work item type, Epic, to better support the Scaled Agile Framework (SAFe).Backlog levels are now optional, so if you aren't using one, you can deselect it. The Epic work item is bound to a new optional backlog level.For more information, see: * [Scaled Agile Framework: Visual Studio Online process template updates](https://blogs.msdn.com/b/visualstudioalm/archive/2015/05/14/scaled-agile-framework-visual-studio-online-process-template-updates.aspx) * [Build preview, updated backlog navigation, branch policies, and more...May 15](https://www.visualstudio.com/news/2015-may-15-vso) * Azure DevOps * Features