Bugfixes

Hi,
I've used your the api wrapper for a project and like it's API. I had to fix some bugs and add some features like calls for whitlists, rejects and templates. There was a bug when sending attachements. Some additional changes were made:

1. AbstractService has been refactored to use https://jersey.java.net/ which makes handling requests and responses easier.
2. There are automated test against Mandrill using a test API-key. Just add mandrill_apikey with an test key to your environment or settings.xml
3. Use Objects.toStringHelper instead of StringBuilder to improve String rendering

Best regards