Moved parameters processors to a new file
Added bd_wordpress_api.response_decorator tag

From now on, response are expected to be from the wordpress API.
Response for other APIs are decorated from the wp ones using
a ResponseDecorator.

Response decorators are services that:
- implementat BD\Bundle\WordpressAPIBundle\ResponseDecorator\ResponseDecoratorInterface
- are tagged as bd_wordpress_api.response_decorator
- provide with a methodName tag attribute with the xml rpc method name

Added implementations for GetPost / GetRecentPosts, and updated post serialization to
match the wordpress API.
Removed unused Controller\MetaWeblog
Refactored mt.getRecentPostTitles
Moved remaining Post actions to their controller