Only check input if the widget provide a value.

Some widgets, formaly dynamics widgets does not provide input values all
time.
Use the "source" parameter instead of "id".
Use the Controller::createClonedModel() when copy a model.
Implementing copy action in parent view for non-manual-sorting listing.
Implement copy in tree view.
Set id to null in Controller::createClonedModel().
In Controller::createClonedModel() clear unique fields.
Merge branch 'release/2.0.0-alpha9'
Merge tag '2.0.0-alpha9' into develop

Version 2.0.0-alpha9