www/rt50: create port

RT is a battle-tested issue tracking system which thousands of
organizations use for bug tracking, help desk ticketing, customer
service, workflow processes, change management, network operations,
youth counselling and even more. Organizations around the world have
been running smoothly thanks to RT for over 10 years.

WWW: http://www.bestpractical.com/rt/

Changelog: https://github.com/bestpractical/rt/releases/tag/rt-5.0.0