* first naive impl
* Unregister sdcard notification
* btngrid reload_items fixed
* format-code
* Avoid some unnecessary updates
* clear empty space after removing items
* Fix displaying sdcard error after inserting card while running
* format code
* Eliminate multiple update_items() calls from on_populate()
And call it only once after on_populate()
* update_items() only once when showing btngrid
* normalize offset when menu item count decreases
E.T.
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