1. add a hook inside tree branches for improved strength
2. fix the issue that interface may fly as a mess (delete the logic
where gap nodes can skip dropping down)
3. fix the issue that base nodes may fly as a mess (smoothing should
skip polygon nodes, see Jira:STUDIO-4403)
Change-Id: Ie9f2039813c2ca3127ed8913304cc455fec8e7ee
(cherry picked from commit 83cef5f91d49ff3d275a89ec3df8b5f0fd573f8c)