#14 reorganize imports and format code
#26 add 3 utility methods to GuiceYars utility class:
 - requiredSuppliers(Injector): returns the suppliers required by the given injector from the registry.
  - providedSuppliers(Injector): returns the suppliers provided by the given injector to the registry.
  - registeredListeners(Injector): returns the listeners registered through the bindYarListener method.

 All those methods returns an empty list if no information is available.