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/sxhkd/sxhkdrc

@@ -1,31 +1,22 @@
 # universal x key bindings
 
 # Open terminal emulator (TODO find way to not hard-code alacritty, perhaps ENV vars)
-mod4 + Return
+super + Return
   exec alacritty
 
 # open quick start menu
-mod4 + space
+super + space
   exec i3-dmenu-desktop
 
 # System functionality
 
 # Enable lock screen (TODO does not stop music, etc yet
-# see https://github.com/LukeSmithxyz/voidrice/blob/archi3/.config/sxhkd/sxhkdrc for that)
 super + x
-  i3lock -e -f -c 1d2021
+  lockscreen
 
-# Shut down system
-super + shift + x
-  dmenuprompt "SHUT DOWN computer?" "sudo -A shutdown -h now" danger
-
-# Exit X session
+# Open System Power Menu
 super + BackSpace
-  dmenuprompt "Log out of X Session?" "i3-msg exit" warn
-
-# Restart system
-super + shift + BackSpace
-  dmenuprompt "Reboot computer?" "sudo reboot" danger
+  rofi-powermenu
 
 # enable function (/media) key functionality
 # TODO: set up next song, previous song, pause, etc