Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

* Remove the heavy-weight virtual flagged mailbox
* Implement a favorites inbox as a simple filtered view
* Refactor the sync logic so it work with filtered mailboxes

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

Co-authored-by: Roeland Jago Douma <roeland@famdouma.nl>
Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>
Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

Bumps [christophwurst/nextcloud_testing](https://github.com/ChristophWurst/nextcloud_testing) from 0.7.0 to 0.9.1.
- [Release notes](https://github.com/ChristophWurst/nextcloud_testing/releases)
- [Commits](https://github.com/ChristophWurst/nextcloud_testing/compare/0.7.0...0.9.1

)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>
Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>