Name the devtool window

When the devtool widget is invoked with "window", it appears in its own
window. Currently the window title is "qutebrowser", preventing
dedicated compositor configuration. We fix this by naming it
"Web Inspector".

qutebrowser/browser/inspector.py

@@ -158,6 +158,7 @@ class AbstractWebInspector(QWidget):
         self._position = position
 
         self._widget.show()
+        self.setWindowTitle("Web Inspector")
         self.show()
 
     def toggle(self) -> None: