show cache on admin overview, add modal to clear cache, re-add logging to policy

passbook/core/views/overview.py

@@ -2,6 +2,7 @@
 
 from django.contrib.auth.mixins import LoginRequiredMixin
 from django.views.generic import TemplateView
+
 from passbook.core.models import Application
 from passbook.core.policies import PolicyEngine