Granular and flexible work breakdown structure

• Support granular and flexible work breakdown structure for issues and epics.
• Have epics of epics, i.e. sub-epics (nested epics).
• View and manage epics and issues at the group level.
• Navigate back up to higher abstraction (higher-level epics, starting all the way at the leaf node (an issue)).
• Integrate with roadmap view to quickly expand/collapse tree structures.