Figure out what to do with "old" notificaitons

[mtwomey]

We don't want them building up in the DB "forever".

Some thoughts:

1. When a Connect project closes, delete all associated notificaitons
2. Delete unacknowledged notifications after some long period of time (like 6 months or something...)

[vikasrohit]

2 Sounds good to me. For 1, I would like to keep a buffer period of 1-3 months after closing of the project before deleting the notifications.