Allow user to order senders in Rollups and improve automatic ordering

[Jivings]

Three parts to this;

1. We should order the senders better, right now if you receive two different subscriptions from linkedin.com they probably wont appear next to each other. It would be good if we could order the list of emails in the Rollup by domain.
2. We should let the user manually order the things in their Rollup. This is especially useful for the featured view.
3. We could offer an option to group the senders in the Rollup by domain, so that eg all the linkedin emails will appear as one item.

[jondkinney]

Thanks for writing this up @Jivings. The main benefit to me would be #3. That way I could click "Read All" to see all the nonsense that LinkedIn sent me in 4 separate emails from 4 separate LinkedIn email addresses by just scrolling through them all at once!