webadmin, userportal: Avoid uncaught exceptions in UiCommonEditorVisitor

If a setter method is missing or has wrong argument type,
EditorContext.setInModel (generated) implementation will
look like this:

    @Override public void setInModel(EDITED_TYPE data) {
        throw new UnsupportedOperationException();
    }

See AbstractEditorDriverGenerator:296 for details.

In above mentioned situation, EditorContext.canSetInModel
(generated) implementation will return false.

In short, we should always call canSetInModel before
attempting to call setInModel, otherwise uncaught
exception might break the application.

Change-Id: I4b7fc601bad9470eab7fbfa0e291f69f2cabae03
Signed-off-by: Vojtech Szocs <vszocs@redhat.com>