[2.2] [FrameworkBundle] [Serializer] Loads the Serializer component as a service in the Framework Bundle

It looks like the Serializer service is not in the Service Container. This PR allows users to get this service through the DIC by just simple doing $container->get('serializer');

Also, by default, the Framework Bundle will load a couple of encoders (JSON and XML) and one normalizer (GetSetMethodNormalizar). If the user wants to add more encoders or normalizer he will just have to tag it, using the specials tags "serializer.encoder" and "serializer.normalizer". 

Bug fix: no
Feature addition: yes
Backwards compatibility break: no
Symfony2 tests pass: yes
Fixes the following tickets: [comma separated list of tickets fixed by the PR]
Todo: If this PR is approved then this file
https://github.com/symfony/symfony-standard/blob/master/app/config/config.yml
should be modified for something like this
https://gist.github.com/3471185
License of the code: MIT