credit label update:

* fix reference to new enum
* add months and years to label

limitmonitor/models.py

@@ -77,7 +77,7 @@ class Limit(models.Model):
 
     def credit_label(self):
 
-        if self.service == "TUNNEL":
+        if self.service == Service.TUNNEL:
             return self.days_credit_label()
         else:
             return self.days_credit_label()
@@ -86,7 +86,13 @@ class Limit(models.Model):
 
         single_day = 60 * 60 * 24
         days = int(round(delta.total_seconds() / single_day))
-        return str(days) + " days"
+
+        if days <= 62:
+            return str(days) + " days"
+        elif days <= 744:
+            return str(days // 30) + " months"
+        else:
+            return str(days // 365) + " years"
 
     def days_credit_label(self):