Usergrid 2291 export to redshift

This PR complete two new Usergrid Tools: WarehouseExport which exports UG data to CSV and then (optionally) uploads that to AWS S3 and WarehouseUpsert which copies same data from S3 into an AWS Redshift database. 

Also there is a new Maven assembly that will create an installable release bundle for Usergrid Tools plus a new README.md that explains how to use Usergrid Tools and goes into detail on the new WarehouseExport and WarehouseUpsert tools. You can see it here: https://github.com/apigee/usergrid-stack/tree/USERGRID-2291-export-to-redshift/tools.