New port: devel/libdbusmenu-qt5.

This is the Qt5 version of devel/libdbusmenu-qt. They both come from the
same tarball, so the differences between both ports are minimal at this
point.

From pkg-descr:

A library that provides Qt5 implementation of the DBusMenu protocol.
The DBusMenu protocol makes it possible for applications to export
and import their menus over DBus.

WWW: https://launchpad.net/libdbusmenu-qt

Submitted by: Tobias C. Berner <tcberner@gmail.com>