Set the X keyboard layout in a file parsable by localectl

The current Cnchi code runs `sed` in the post install script to set the xkblayout in /etc/X11/xorg.conf.d/10-evdev.conf. In systemd-based systems, this should be set in /etc/X11/xorg.conf.d/00-keyboard.conf, which is where the `localectl` expects the xkblayout settings to be.

This pull request changes Cnchi so that it writes /etc/X11/xorg.conf.d/00-keyboard.conf in a format understandable by the systemd `localectl` tool.