sysutils/nmdaemon: add new port

This is a daemon that manages network configuration of FreeBSD.

The daemon can manage:

• some system network parameters
• interfaces
• routes
• wireless networks (using wpa_supplicant)

nmdaemon should be started as root, it opens a unix socket where
clients can connect. The permissions of the unix socket are managed
by nmdaemon and provided by it's configuration file.

To communicate with nmdaemon one should use JSON formatted commands,
nmdaemon answers with JSON formatted data too.
The syntax and examples of the commands can be found in commands.md.

The Makefile and pkg-descr files have been made compliant with
FreeBSD conventions by me (pkg-descr is derived from README.md).

Pull Request: https://github.com/freebsd/freebsd-ports/pull/224