PocketBook: Auto-standby plugin (#6602)

Adaptively pins the auto-standby UI lock. When frequent input
from user is observed, we'll prevent for increasingly longer
periods of time, and revert back to more aggressive standby
with infrequent input (infrequent taps when reading a book).

frontend/ui/elements/reader_menu_order.lua

@@ -61,6 +61,7 @@ local order = {
         "keyboard_layout",
         "time",
         "battery",
+        "autostandby",
         "autosuspend",
         "autoshutdown",
         "ignore_sleepcover",