Clarity: add missing abstract methods _on_shutdown and initialize (issue #113)

* microscope/filterwheels/aurox.py (Clarity): class was missing an
  implementation for the Device abstract methods _on_shutdown() and
  initialize().  This was working before because when we migrated to
  Python 3 we messed up the implementation of ABCs.  That was fixed
  with 83f1256 so all Device classes that don't implement the
  whole interface were failing since.

Author: Ian Dobbie

microscope/filterwheels/aurox.py

@@ -262,3 +262,9 @@ def set_position(self, pos, blocking=True):
         while blocking and self.moving():
             pass
         return result
+
+    def _on_shutdown(self):
+        pass
+
+    def initialize(self):
+        pass