Add Ability to globally disable Notifications

[KevinJump]

sometimes you might want to turn off all notifications from Translation manager.

You can turn off most by simply not setting email addresses inside the translation set notification settings, but the author of a job will always get a notification when a job is received.

This feature will let you turn them off globally in the appsettings.json file

"Translation" : {
   "Notify" : {
         "Disabled" : true
    }
}