Support RFC 5256

[tristan957]

I use the bridge with my Proton email account. Unfortunately, the bridge doesn't support RFC 5256, which makes it extremely difficult to make use of all the features of my client. I also experience a large usability issue in that when viewing emails in my client, they are sorted by UID instead of date, which causes me to view messages out of order.

I originally opened an issue in the bridge repository, but then noticed that it uses gluon for the imap server.

Prior art would be https://github.com/emersion/go-imap-sortthread.