DynamoDB Store prototype

[tb06904]

Describe the new feature you'd like
A basic prototype for a Gaffer Store that connects and stores data in AWS's DynamoDB.

Why do you want this feature?
Provides a cloud native storage option for Gaffer rather than Hadoop/Accumulo which can be difficult to deploy on the cloud.

Additional context
Just a simple proof of concept should be enough to see if Gaffer can use the key value storage of DynamoDB.