Optimizer rule for TopN (#279)

* add TopN PlanNode and Executor

* add topn rule

* fix topn rule

* fix auto

* add topn rule test

* fix indent

* fix conflict

* fix conflict

* fix ;

* add newline

* fix colNames

* update code

* update code

* fix static function naming style

* fix name

* fix name

* check result data in test_optimzier

* fix