Accept packages with new structure using xpdo3

[muzzwood]

Using the new xPDO v3 style package structure relies on using the new options:

• namespace
• model

And class should be changed to the fully qualified class name.

As an example for CollectionSetting in the package Collections, you'd use the following:

collections_settings:
        namespace: Collections
        model: Collections\Model
        class: Collections\Model\CollectionSetting
        primary: id
        package: collections

You can also specify a custom path as before using package_path. Otherwise the new default will be used. The new default is src instead of model.
e.g.

core/components/package/src/

[muzzwood]

Example for FormaliciousFieldType extract/build:

formalicious_fields_types:
        namespace: Sterc\Formalicious
        class: Sterc\Formalicious\Model\FormaliciousFieldType
        model: Sterc\Formalicious\Model
        primary: id
        package: formalicious