games/dxx-rebirth: update to 20190523

Update to 20190523. Upstream also changed its naming convention.
Change mainainer to my @FreeBSD.org address.
Sort USES, add USES=sdl tar:xz (tarball switched to xz).
Add patches from https://github.com/dxx-rebirth/dxx-rebirth/pull/426

Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D20425