New port: net/nncp: Utilities for secure store-and-forward files and mail exchanging

More information is here: http://www.nncpgo.org/

PR: 215973
Submitted by: Sergey Matveev <stargrave@stargrave.org>
Approved by: tcberner (mentor), mat
Differential Revision: https://reviews.freebsd.org/D13700