Complete Notification Settings

[orenyk]

We've been asked by the Law admins to disable the overdue check-in e-mails for their patrons since they don't really have due dates / late fees. While we can add a setting to disable this specific e-mail, I think we should update our notification settings to include all possible user and admin mailers to allow for greater admin control over what e-mails get sent. I don't think we necessarily have to allow for the e-mail bodies themselves to be customizable for all notifications as we currently do for the e-mails in the app settings, but on-off toggles for both the user and the admin for each message would be nice.

[orenyk]

Just realized that this is a duplicate of #485, closing!

[orenyk]

This is a better bucket issue, reopening.