net-im/nchat: update: 5.14.44 -> 5.15.26

The themes installation has been removed for some reason, and because
of their usefulness it's better to resurrect such functionality. In
addition to that, add templates installation as well.

ChangeLog: https://github.com/d99kris/nchat/compare/v5.14.44...v5.15.26

Sponsored by: tipi.work