Model utils: setData should load data and set selection in the editor in such a way that they are rendered

[Reinmar]

Related to https://github.com/ckeditor/ckeditor5-engine/issues/441.

Currently setData() just inserts the data into the model, but not in a way that would trigger rendering the content. It should use a similar method as here in the tests: https://github.com/ckeditor/ckeditor5-engine/blob/1a79448aa15cd1692cc02a1589ed945fc9823cf5/tests/editingcontroller.js#L139-L149

[Reinmar]

This issue is very important, because every single feature which introduces some converters will want to use this method.

[Reinmar]

As a workaround I'm planning to use the data pipeline. That's not going to allow me to set the selection and analysing the code will be harder because you will load data which will be transformed to model and then to view. But other than that, this method will be enough.

[Reinmar]

This method should work like the DataController.set() method.