Only show the link to use list if service has lists

Most services won’t be interested in the contact list feature, so we
shouldn’t clutter up the interface with the extra link.

app/models/service.py

@@ -6,6 +6,7 @@ from notifications_utils.timezones import local_timezone
 from werkzeug.utils import cached_property
 
 from app.models import JSONModel
+from app.models.contact_list import ContactLists
 from app.models.job import (
     ImmediateJobs,
     PaginatedJobs,
@@ -695,3 +696,7 @@ class Service(JSONModel):
             for report in self.returned_letter_summary
             if parse(report['reported_at'] + " 00:00:00") >= seven_days_ago
         )
+
+    @property
+    def contact_lists(self):
+        return ContactLists(self.id)