Use configuration element to determine implementation for ObjectWithFields in same way as Collections

Currently the CollectionConverter uses the configuration element for the parameters to determine the implementation of the
elements that go in the collection.

For instance, a field declaration like 'private List someThing;' in package.SomeComponent
will trigger a check for the existence of class package.SomeThing.

We should be able to do the same for other complex types:

private SomeInterface someImpl;

will trigger a check for ...SomeImpl.