Update stream_viewer to support new Neptune streams features

[krlawrence]

The 1.1.0.0 release of Amazon Neptune adds a iteratorType=LATEST parameter to the stream to find the most recent transaction and operation on the stream. The %stream_viewer magic should be updated to utilize this. Further, there is now a timestamp available in the stream for each transaction. That information should be added to the stream viewer widget.

[krlawrence]

The 1.1.1.0 Neptune release further adds adds an indicator when an operation is the last one for each transaction. Now would be a good time to work on these updates. These features are version specific so we will need a strategy for determining which ones are available on the Neptune instance that a notebook is talking to.

[krlawrence]

Initial commits to add the timestamp
59eba4b
9099e6c

[krlawrence]

The commits made so far address the isLastOp and timestamp new features. The remaining work is to update the stream viewer code to use the iteratorType=LATEST if supported. As this is not something visible to the end user, we can release the other improvements independently of that remaining piece of work.