Remove unused imports
Implement methods to display tokens on view

* In PipeController create empty petrinet with default token
* In PetriNetController implement methods to increment tokens
* Still need to show tokens based on model rather than creating in
  the view drop down
* There's a bug when you open a new petrinet the active petrinet is stuck
  to the latest opened, so swapping back to an old net won't add any places.
  Need to fix this up!