[IMAPx] Support RFC 6855 (IMAP Support for UTF-8)
When Evolution tries to fetch an email with unencoded UTF-8 characters in the Subject: line, an RFC6855 compliant server (Courier IMAP in my case) does not return the message. It seems likely from a quick glance at RFC6855 the "ENABLE UTF8=ACCEPT" command is not implemented, but I could easily be wrong about that as I am not familiar with code. I am running Evolution 3.28.5 on Fedora 28 and using Courier 1.0.0-20180927 mail server.