Fix box layout to use entire window

companion/app.py

@@ -33,7 +33,3 @@ class MynitCompanionApp(App):
 
     def update_device_list(self, devices):
         self.widget.update_device_buttons({device.getAddress(): device for device in devices})
-
-    def build(self):
-        self.widget = DeviceListWidget()
-        return self.widget

companion/mynitcompanion.kv

 #:kivy 1.0.9
 
-<DeviceListWidget>:
+DeviceListWidget:
     device_buttons: device_buttons
 
     BoxLayout:
         orientation: "vertical"
+        size: root.width, root.height
+
         Label:
             text: "Device List"