[WIP] Introduce symfony service container and testwork extensions

Starts to replace the custom container with the Symfony one. Its wrapped inside it at the moment with a view to just having the symfony container in a later major version. As a result of trying to maintain b/c its quite hacky at the moment and would require quite a bit of clean up at a later stage.

Supports both current phpspec extensions and testwork extensions. Started moving some of the core services to testwork extensions. 
you should use a special prefix on the tag name for service id prefixes, to avoid conflicts with other tags added when using the Symfony container directly (in Testwork extensions directly)