+ H2H Manager: not a singleton/enum anymore, regular class
+ Replaced all H2HManager.INSTANCE's with member variable of classes
- removed RegisterValidation class (logic is integrated in the register
controller with field validation)
NOTE: H2H manager instance not passed through controllers yet.
+ Dependency injection with Guice
Controllers get H2Hmanager injected by Guice at construction time
~ Added missing @Inject annotation
+ added Guice bindings for the controllers
~ Refacotred the createNode methods (they both do the same now)
+ Created user manager and extracted user management related methods
such as register and login into own class
+ Root path: removed the navigate to login view call and return a
boolean indication verification
+ Refactoring of navigation service (extracted fxml loader logic)
+ Added class with constants for each view name (instead of strings)
+ Renaming views using consistent scheme (...View instead of Window)
+ Unit tests adapted (H2H Manager instance instead of singleton)