Create a post-deployment migration to update all existing notification settings
with at least one custom level enabled to the new format. Also handle the same
conversion when updating settings, to catch any stragglers.
If the Sidekiq job fails for some reason, a project can be 'stuck'
pending deletion. The project can't be viewed, so it shouldn't be
available through the notification settings association as this will
throw an exception when we try to show the link.
It will hold notification setting per group or per project. It will
allow get rid of notification level stored in Member model
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
