Moving extension to be in line with the symfony standards

The extension naming should follow the [docs][0]
                                                                                
> If you do choose to expose a semantic configuration for your bundle, you'll first need to create a new "Extension" class, which will handle the process. This class should live in the DependencyInjection directory of your bundle and its name should be constructed by replacing the Bundle suffix of the Bundle class name with Extension. For example, the Extension class of AcmeHelloBundle would be called AcmeHelloExtension

[0]: http://symfony.com/doc/current/cookbook/bundles/extension.html#creating-an-extension-class