[WorkInProgress] Start integration of Symfony DependencyInjection Container.

This is a first attempt to integrate the Symfony DependencyInjection Container into PDepend, allowing it to fetch the TextUI Runner from a predefined services.xml:

The following Todos need to be evaluated before merge:

* Move more logic from Command to the Application and building process, probably by the means of an Symfony DIC Extension
* Tests for the container building process
* A mechanism to overwrite the service container definitions with the pdepend configuration file