* Properly check nbf and exp claims in token to determine simple
validity.
* Properly check nbf and exp claims in validator and throw exceptions
if expired/not yet valid.
* Use requireIssuer() and requireAudience() on the JwtValidator to make sure
that the token is for what you expect it to be for.
* A setAll() method has been added to property bag, applying but not overriding
values.
* Added tests for JwtValidator.
