Rebuild bundle config

[jdreesen]

When I wanted to implement #39, I realized that the current bundle configuration does not really allow configuring different converter types (as already described in #40). It is possible to specify any converter class, but it must have the exact same constructor parameters as the class GenericConverter. This is not the case with the StrategicConverter, so that the current configuration is not suitable for this type.

Therefore, here is the proposal of an implementation that allows arbitrary converter types. Instead of defining the class, the type is now specified by means of a keyword and the corresponding configuration is nested underneath.

The advantage is that the configuration per type is freely definable. In addition, this allows the configuration to be extended by other bundles or the app.

Current:

neusta_converter:
  converter:
    person.converter:
      converter: Neusta\ConverterBundle\Converter\GenericConverter
      target_factory: Neusta\ConverterBundle\Tests\Fixtures\Model\PersonFactory
      populators:
        - Neusta\ConverterBundle\Tests\Fixtures\Populator\PersonNamePopulator

Proposed:

neusta_converter:
  converters:
    person.converter:
      generic:
        target_factory: Neusta\ConverterBundle\Tests\Fixtures\Model\PersonFactory
        populators:
          - Neusta\ConverterBundle\Tests\Fixtures\Populator\PersonNamePopulator

---

However, it is not yet entirely clear how decorating converters fit into this scheme. Currently, only exactly one converter type keyword is allowed. One consideration would be to create a new interface for decorating converters and to allow several decorating converters in addition to the one main converter, like:

neusta_converter:
  converters:
    person.converter:
      generic:
        target_factory: Neusta\ConverterBundle\Tests\Fixtures\Model\PersonFactory
        populators:
          - Neusta\ConverterBundle\Tests\Fixtures\Populator\PersonNamePopulator
      cached:
        key_factory: YourNamespace\UserKeyFactory