Add tuple-event-time ordered time-based windows

TStream.last(period,unit,keyFn) creates an insertion-time time-based TWindow - a tuple's timestamp, hence its lifetime in the time-based window, is based on the time it is inserted into the window.

On a couple of occasions some folks have asked about event-time time-based windows - a tuple's timestamp (event-time) is present as a property in the tuple and that timestamp is used for insertion and eviction processing. Tuples need not be added to the window in their event-time order though the partition contents are maintained in event-time order.

The TStream API for such a time-based window could be:
```
<K> TWindow<T, K> last(long time, TimeUnit unit, Function<T, K> keyFunction, ToLongFunction<T> timestampFn);
```

See also: QUARKS-230