new port: x11-themes/matcha-gtk-themes

Matcha is a flat Design theme for GTK 3, GTK 2 and Gnome-Shell which supports
GTK 3 and GTK 2 based desktop environments like Gnome, Unity, Budgie, Pantheon,
XFCE, Mate, etc.

PR: 247046
Submitted by: Alexander88207@protonmail.com (maintainer)
Differential Revision: https://reviews.freebsd.org/D25176