* Unify `set_feed_variable` to one method

* Move global scope to python, not in C++

* Delete kid

* Delete local scope

* remove alias

* Make interface of Operator to `const Scope&`

* Refine unittest also

* ScopePtr means pointer of scope, but it can be shared or uniqued.
Change it to std::shared_ptr<Scope> to make code better to read.

* use OperatorPtr = std::shared_ptr<OperatorBase>;
* use ScopePtr = std::share_ptr<Scope>;