Adds tasks for round tripping JWT tokens, making testing and deployment easier.

This set of changes adds two ant tasks that produce and consume JWT tokens and thus provide a mechanism to check a web-app's configuration before deployment. It also includes some fixes to the JWT verification logic and the ability to generate JWT tokens for external and internal consumption.

It also allows users to provide public keys to be used for verification in properties files if they wish (see discussion with @vivekkrish)

It also includes tests for the new code, including tests for generating key-stores.