Add JwtHelper.header() convenience method to access headers

Exposes the headers as a map to facilitate key rotation (you look
in the header for a "kid" before you call decodeAndVerify()).

Update bouncy castle to 1.55 for 1.0.6

Update to 2.0.12 for release

Release 2.0.11

Update to 2.0.10

Update to 2.0.9 for release

Allow custom authentication filters for the TokenEndpoint.

These filters are added upstream of the traditional
BasicAuthenticationFilter.

Simple integration test project added, details in README.md.

Fixes spring-atticgh-601, fixes spring-atticgh-602

Bump versions for 2.0.7