Doctrine PHPCR Config

Added Doctrine PHPCR Config via PrependExtensionInterface. Now you can use all the doctrine:phpcr commands.

- [x] finish the code
- [ ] gather feedback for my changes


| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| Tests pass?   | none
| Fixed tickets | #31 
| Doc           | none