Gui: Extend TaskDialog

* Add TaskDialog::autoClosedOnDeletedDocument()
* Add option to automatically close task dialog when document is deleted
* Expose autoClosedOnDeletedDocument() to Python
* Expose autoClosedOnTransactionChange() to Python
* Change ControlPy::showDialog() to directly return the task dialog wrapper
* Change TaskView::slotDeletedDocument() to close task dialog if requested

src/Gui/TaskView/TaskDialog.cpp

@@ -93,10 +93,7 @@ bool TaskDialog::canClose() const
     msgBox.setStandardButtons(QMessageBox::Yes | QMessageBox::No);
     msgBox.setDefaultButton(QMessageBox::Yes);
     int ret = msgBox.exec();
-    if (ret == QMessageBox::Yes)
-        return true;
-    else
-        return false;
+    return (ret == QMessageBox::Yes);
 }
 
 //==== calls from the TaskView ===============================================================
@@ -116,6 +113,11 @@ void TaskDialog::autoClosedOnTransactionChange()
 
 }
 
+void TaskDialog::autoClosedOnDeletedDocument()
+{
+
+}
+
 void TaskDialog::clicked(int)
 {