AMQP-300 Add Jackson2 Message Converter

AMQP-300 Polishing

Add tests for missing coverage (both Jackson versions).
Merge pull request #88 from aspan/AMQP-300
AMQP-300 Add Jackson 2.x to What's New
AMQP-304 Close Rabbit Connections in Tests

For reference see: https://jira.springsource.org/browse/AMQP-304

Polishing
Merge pull request #89 from ghillert/AMQP-304