Updated backup_menu with 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/backup_menu.sh

@@ -14,7 +14,7 @@ backup_ui(){
   echo -e "|  2) [Moonraker]        |  Other:                      | "
   echo -e "|  3) [Moonraker DB]     |  7) [Duet Web Control]       | "
   echo -e "|                        |  8) [OctoPrint]              | "
-  quit_footer
+  back_footer
 }
 
 backup_menu(){
@@ -40,11 +40,11 @@ backup_menu(){
         do_action "backup_dwc2" "backup_ui";;
       8)
         do_action "backup_octoprint" "backup_ui";;
-      Q|q)
+      B|b)
         clear; main_menu; break;;
       *)
         deny_action "backup_ui";;
     esac
   done
   backup_menu
-}
+}