tests for and refactoring of [Queue] - this libraries first composite type ...

... [Queue] types can be created from different [QueueFactory] module implementations.

- every queue will be able of [enqueue]-ing and [dequeue]-ing items of any type.
- every queue can be subscribed to and does dispatch its own "enqueue", "dequeue" and "empty" events.

- the [Queue] type already is completely covered by tests.
- the different [QueueFactory] modules are not completely covered yet.