Scopes should be like bubbles, automatically expanding as members are added

[forrestbao]

Currently, a scope is visualized as a large box, even when it is empty. This is not good. It takes too much space. Manual enlargement is needed when it members grow into too many. And vise versa for manual shrinkage when removing a member.

So I suggest let a scope be initially a small round-cornered rectangle. A member, which can be either a code cell or a scope, can be added into the scope by drag-and-drop. After drag-and-drop, the scope should expand itself to slightly but tightly fit the member(s).