Expose approximateArrivalTimestamp through the KinesisDeserializationSchema interface

Amazon's Record class also gives information about the timestamp of when Kinesis successfully receives the record: http://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/services/kinesis/model/Record.html#getApproximateArrivalTimestamp().

This should be useful info for users and should be exposed through the deserialization schema.