Adjust dummy detector for generalized base

concert/devices/detectors/dummy.py

@@ -8,6 +8,14 @@ class Detector(base.Detector):
     """A dummy detector."""
 
     def __init__(self, camera=None, magnification=None):
-        camera = Camera() if camera is None else camera
-        magnification = 3 if magnification is None else magnification
-        super(Detector, self).__init__(camera, magnification)
+        self._camera = Camera() if camera is None else camera
+        self._magnification = 3 if magnification is None else magnification
+        super(Detector, self).__init__()
+
+    @property
+    def camera(self):
+        return self._camera
+
+    @property
+    def magnification(self):
+        return self._magnification