Toggle menu for PSU from LCD pannel

From the prepare menu, accessible when is not printing, you have the
possibility to turn off the PSU when is on et vice versa.
From the host, you can turn off or turn on the PSU then the menu is
updated accordingly.
From the LCD message, the printer status is reported ready or off
respectively when the PSU is on or off.
Turn off power supply off-load

Disable the high current output and wait a little before to turn off,
because the interrupting capacity of the PSU is unknown.
Could be a function if needed by other.
No bed config for RAMPS

The motherboard 35 is a config without bed with this pins setting :
D8 Extruder
D9 Fan
D10 Controller Fan