games/openjk: Community effort to maintain Jedi Academy + Jedi Outcast

OpenJK is an effort by the JACoders group to maintain and improve the game
engines on which the Jedi Academy (JA) and Jedi Outcast (JO) games run on,
while maintaining full backwards compatibility with the existing games.
This project does not attempt to rebalance or otherwise modify core gameplay.

WWW: https://openjk.org

PR: 227265
Approved by: mat (mentor)
Differential Revision: https://reviews.freebsd.org/D19955