Cleanup/Simplify/Todo

Cleanup/Simplify/Todo
* Tracker_field, Tracker_list: Added dispose() to clear some static variables. -- When you create-and-destroy some instances of a class serially without dispose, they will use the same static variable causing side-effects. Note you should not use static variables if you can. When you create multiple instances of a class simultaneously, they will use the same static variables causing terrible side-effects.
* Remove unused arguments
* Less grobal variables