Saved search email improvements [MJ-895, MJ-896]

- Add activation link to saved searches of inactive users
- Send saved searches to inactive users
- Add activation window countdown

I changed the counter when there is less than one day remaining from "In X days, your activation window will expire" to "Your activation window will expire today". I thought that might be more pleasing than the alternative.

I think we could draw more attention to these. Maybe have the counter in red or something.

All tests pass.