make sure windows that are minimized are restored (#853)

aqt/__init__.py

@@ -44,6 +44,7 @@ class DialogManager(object):
     def open(self, name, *args):
         (creator, instance) = self._dialogs[name]
         if instance:
+            instance.setWindowState(Qt.WindowActive)
             instance.activateWindow()
             instance.raise_()
             return instance