Bug1043

Removed the option that an user can choose to receive notifications by email or private messages. Also removed by complete the attribute :notification and all of your occurrences. 
You shouldn't change migrations. This is something that was already applied to all databases, changing things here won't have any effect in the servers.
Revert this one back to how it was and make a new migration that removes the column `notification`. Take a look at [this migration](https://github.com/mconf/mconf-web/blob/master/db/migrate/20140120194243_remove_event_id_from_attachments_and_posts.rb) for an example.