Use heartbeat frequency for currently active

If the heartbeat frequency is more than 10 seconds, shynet will display as not active, even though it still is.

Using 2x the heartbeat frequency should give better results.

shynet/analytics/models.py

@@ -1,6 +1,7 @@
 import json
 import uuid
 
+from django.conf import settings
 from django.db import models
 from django.shortcuts import reverse
 from django.utils import timezone
@@ -57,7 +58,7 @@ class Session(models.Model):
 
     @property
     def is_currently_active(self):
-        return timezone.now() - self.last_seen < timezone.timedelta(seconds=10)
+        return timezone.now() - self.last_seen < timezone.timedelta(milliseconds=settings.SCRIPT_HEARTBEAT_FREQUENCY * 2)
 
     @property
     def duration(self):