Play Dead mode

The purpose of the Play Dead mode is to fake a blocking error to prevent a suspecting person to inspect and guess what the other modes do. It's easily enabled from the main menu, and disabled with a programmable key sequence (see Setup menu).

The PortaPack will keep playing dead even after a power cycle, the only way to exit the mode is to enter the "secret" key combination entered in the Setup menu -> Play dead and pressing select. (It is also possible to exit the mode by reprogramming the device or removing the backup battery for a few minutes).

The key combination has a max length of 10 directional key presses.

If no exit key sequence was programmed, it defaults to up-down-left-right. Enter the sequence and press select, you should see "Please reset" appear. After reset, you should be able to go back to the main menu. If not, a sequence was probably entered already. Solution hint: ctrl+F for 0x8D1 in ui_navigation.cpp ;)

This mode can also be used as a login screen (see Setup menu).

TODO: When Amnesia is enabled, entering the play dead mode will erase the battery-backed RAM (last tuned-in frequency, settings...).