- This work is a prerequisite for #1290 and #1289
- Create an `EmailData` model which holds email counts per
(CommitAuthor, Version).
- Add management command `sync_mailinglist_stats` to query data from the
hyperkitty database and build `EmailData` objects from it
- EmailData.count is calculated between x.x.0 release_dates
- Add button in EmailData admin to trigger task
- Update the `merge_author` method to update EmailData with the Summed
counts per version and delete EmailData which pointed to the
`CommitAuthor` being merged from.
