Issue #, if available:

Description of changes:
Added new events DynamodbTimeWindowEvent and KinesisTimeWindowEvent for supporting stream analytics.
Added a couple of event response classes. StreamsEventResponse will be used to report batch item failures for Kinesis and Dynamodb events. TimeWindowEventResponse will be used for returning the stream analytics state as well as reporting batch item failures for KinesisTimeWindowEvent and DynamodbTimeWindowEvent.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.