Add mail/dovecot22 (v2.2.35) and mail/dovecot-pigeonhole04 (v0.4.23)

This brings back Dovecot 2.2.35 to the tree because there is an issue
with version 2.3.1 and replication in some scenarios [1].

Keep this version until this problem gets fixed upstream.

1 - https://www.dovecot.org/list/dovecot/2018-April/111477.html

Approved by: adamw (maintainer of mail/dovecot)
Approved by: ler (maintainer of mail/dovecot-pigeonhole)