Add x11/keybinder-gtk3

Keybinder is a library for registering global keyboard shortcuts.  Keybinder
works with GTK-based applications using the X Window System.

WWW: https://github.com/engla/keybinder


git-svn-id: svn+ssh://svn.freebsd.org/ports/head@366189 35697150-7ecd-e111-bb59-0022644237b5
- Pass maintainership


git-svn-id: svn+ssh://svn.freebsd.org/ports/head@366190 35697150-7ecd-e111-bb59-0022644237b5