Automatic filesystem discovery and removal

[vit9696]

It will be useful to automatically show boot options from inserted drives and remove the boot options that were detached. The former could be achieved by adding an event registered to simple fs installation. The latter will most likely require timer-based handle validity checking.

I.e. When I insert a USB key I would like it to be recognised and displayed in the picker automatically without having to press ESC. Same with removing the USB key. This is what Apple Boot Picker does. The change would require changes on the UI side as well.