Add a lambda handler to make change replication callable as a lambda function

[marcocitus]

We could make the change replication in Podyn callable as a Lambda function by implementing a RequestHandler per the example in: http://docs.aws.amazon.com/lambda/latest/dg/with-dynamodb-create-package.html#with-ddb-example-deployment-pkg-java

Podyn is already packed in the right way for lambda functions (as a shaded JAR).