Disable the collection of metrics when not deployed

We were using up a lot of events in our dev environments.

(imported from commit 8413ecfa835cce0a231bdf437f37ad8cf12a9133)

zephyr/context_processors.py

@@ -11,4 +11,5 @@ def add_settings(request):
 def add_metrics(request):
     return {
         'mixpanel_token': settings.MIXPANEL_TOKEN,
+        'enable_metrics': simplejson.dumps(settings.DEPLOYED),
     }