ModelImportWizard.doImport does not import the model to specified target

When triggered from the UI the target should always be the project
resource. Otherwise any target resource should be accepted.
DefaultPasteImportAdvisor must be used instead of the
ModelImportAdvisor, since ModelImportAdvisor always replaces the target
with the project resource (to support copy-pasting of models in UI).

refs #7418

Change-Id: I1b7eaef30ab32154319822c0615b9ab96a3f70b6