[RX51] Add support for physical events w/ acpid

This adds a way to handle physical events like keypad slide switch, screen lock, camera lid, and others. This uses acpid from busybox (I was wrong about the real acpid package), and an acpi.map file to map events to 'scripts'. The scripts are symlinked to /etc/acpi/handler.sh, automatically by the new post-install script, where they are handled based on which script was called. This allows for easily adding whatever is necessary for #178 (closed).

If this PR is merged, I will create a new wiki page detailing how others can use this framework on other devices.