[new] stalwart-jmap & stalwart-imap: JMAP server written in rust

hi,

here's two new wip ports for https://jmap.stalw.art/ and its counterpart
https://imap.stalw.art/ which serves as an IMAP proxy in front of the
JMAP server.

cf https://jmap.io/software.html for more details about JMAP.

i've had quite a struggle with some rust bits but in the end it builds,
packages and starts fine. Not properly tested yet, as its mandatory to
setup TLS certs for it.

it cant work yet with the mail/meli submission i've sent but it's being worked
on upstream.

as for the uids ive reused the ones from prelude/pfflowd:

561 _rbldns _rbldns net/rbldnsd
562 _smokeping _smokeping net/smokeping
563 _postgrey _postgrey mail/postgrey
-#564 _prelude _prelude security/prelude
-#565 _pfflowd _pfflowd net/pfflowd
+564 _stalwart-jmap _stalwart-jmap mail/stalwart-jmap
+565 _stalwart-imap _stalwart-imap mail/stalwart-imap
566 _tor _tor net/tor
#567 _dk-milter _dk-milter mail/dk-milter
568 _milter-greylist mail/milter-greylist

feedback welcome ! especially on the rust bits (the ones about the
bundled zlib are hairy)

Landry