* Update some test descriptions in notifications_spec
The descriptions of these tests didn't actually match the test's assertions!
* Add welcome_notifications column to users table
Also ensures that welcome_notifications cannot be set to `nil`.
* Show an opt-out message for Welcome broadcast notifications
* Add opt-out link to notifications + welcome notification box to settings
* Allow welcome notification subscription to be updated
* Add tests for unsubscribed to welcome notification users
Also refactor generator specs a bit.
* Fix up paths, copy, tests
Use rails path helpers instead of hardcoding paths. Improve copy in a few locations.