Make double start-up hard-reset optional

[pachpict]

Default to a start up which just goes to blank. Revert to double hard reset at start-up if zero key is pressed at start-up.

This likely requires memory of previous display state at shutdown. Pi Canute-UI to flash that to FW memory (as the start-up happens before Pi is connected it cannot read from Pi or external media) when shutdown is initiated. Delete that display state info when Pi does start. If no display state info present in FW memory on start-up then revert to double hard-reset behaviour, as though zero had been pressed (as there was probably an improper shutdown).