x11-toolkits/gtk-session-lock: add new port
This is a library to use GTK 3 to build screen lockers using the
secure ext-session-lock-v1 protocol. This Library is compatible with
C, C++ and any language that supports GObject introspection files
(Python, Vala, etc, see using the library below).
This library is a fork of the incredible gtk-layer-shell, which has
laid all the groundwork necessary to make this happen.