Changed Companion and PIDTable interface

* Companion.push_stack/1 has is now push_stack/2 (binding, scope)
* PIDTable.get/1, finish/1:
  - get/0, finish/0, using the gen_server message sender as pid.
  - get/1 still exists for usage on Controller.
various debugger fixes and minor changes

* PIDTable no longer counts state stack, Companion
  exits by itself if pop_stack is called on an empty stack.