[Reviewer: Alex] Add memento sip events

Alex, can you please review these changes to include the memento sip events
I assume this will be formatted like 20140508122400. However I suspect we will struggle to do much better. At the very least I would explain the formatting, e.g.  

```
Removing calls older than: {{ var_data[1] }} (in YYYYMMDDHHMMSS format)
```