Configure rofi-powermenu and lockscreen script

Use rofi-powermenu to show options for suspend,reboot, shutdown,
lockscreen, log out. Can be invoked with <M-backspace>. Other power
option shortcuts have been removed from quick access through sxhkd or
i3. Lockscreen can still be quickly set with <M-x>.

Lockscreen now resides in its own script to provide one source of truth,
and in case it is further customized in the future.

.config/rofi/modes/rofi-powermenu

@@ -1,37 +0,0 @@
-#!/usr/bin/sh
-
-rofi_command="rofi -theme themes/powermenu.rasi"
-
-### Options ###
-power_off=""
-reboot=""
-lock=""
-suspend_btn="鈴"
-logout_btn=""
-# Variable passed to rofi
-
-chosen="$(printf "%s\n%s\n%s\n%s\n%s" "$power_off" "$reboot" "$lock" "$suspend_btn" "$logout_btn" | $rofi_command -dmenu -selected-row 2)"
-case $chosen in
-$power_off)
-	printf "poweroff"
-	# systemctl poweroff
-	;;
-$reboot)
-	printf "reboot"
-	# systemctl reboot
-	;;
-$lock)
-	printf "lock"
-	# light-locker-command -l
-	;;
-$suspend_btn)
-	printf "suspend"
-	# mpc -q pause
-	# amixer set Master mute
-	# systemctl suspend
-	;;
-$logout_btn)
-	printf "logout_btn"
-	# i3-msg exit
-	;;
-esac