Refactor createArc method into several smaller methods

* It's not clear what this code does
* This is the first step to improving the code, making it more
  readable
* Needs a lot more work
Remove _selectedTokenTypeNumber from PetriNetView

* It was nver used
Reformat simpleNet.xml
Use a StringBuilder for simple xml file & minor refactor
General refactoring #8

* Split code chunks into smaller methods
* Initialise variables when declared
* Improve readability
* This reduces code duplication
* Reduces code duplication between constructors
* MarkingView makes use of Marking setCurrentMarking int call
* Do not use +"" to convert to String, Integer.toString() is better
* Marking setCurrentMarking(int) now calls setCurrentMarking(string) to
  avoid code duplication
* Remove duplicated code by calling constructor from
  Marking(Token, int) ctr
* Add TODO To look into float conversion
* Remove medium copy before calling setWeight, the method
  takes care of this itself
* Remove commented out code, it's version controlled so not needed
* Add a few TODOS to investigate into
Address issue #8, fix bug in renaming myPath to path
 Rewrite TransitionView past logic and add test

 * References #8 and #5
 * Uses mockito to mock PetriNetView
 * Adds unit tests to check pasting of name
Tidy up naming and remove commented out code

* References #8
jere: created foo
jere: merged refactor into develop