Updated update_menu.sh to have back_footer

When I first ran the code, I went to advanced because I had klipper already installed and I wanted to see if I could install fluidd using this code base.
So when see advanced menu I was concerned that "quit" meant quitting the tool instead of exiting the advanced menu. So proposing a back_footer for sub menus that will revert back to main menu. Save quit footer for main menu to exit program.

scripts/ui/update_menu.sh

@@ -24,7 +24,7 @@ update_ui(){
   echo -e "|  8) [PrettyGCode]      |  $LOCAL_PGC_COMMIT | $REMOTE_PGC_COMMIT | "
   echo -e "|                        |------------------------------| "
   echo -e "|  9) [System]           |  $DISPLAY_SYS_UPDATE   | "
-  quit_footer
+  back_footer
 }
 
 update_menu(){
@@ -55,7 +55,7 @@ update_menu(){
         do_action "update_system" "update_ui";;
       a)
         do_action "update_all" "update_ui";;
-      Q|q)
+      B|b)
         clear; main_menu; break;;
       *)
         deny_action "update_ui";;