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
Added CUSTOM_MENDEL_NAME option to Configuration.h and language.h

Also cosmetic comment changes and spelling corrections in printed
messages
Make M303 silent when "S0" is sent

If S is left out perhaps it should be silent, but check the spec for
this M code.
Support for 10 level deep SD folder hierarchy
Adding servo documentation
Report temperatures for all extruders
Apply all changes from latest Marlin_V1

Diffed and merged, preserving my updates
Update Configuration.h
Update pins.h
Update language.h
Update Configuration.h
Update Configuration.h
Update pins.h
Make the beep tone less offensive
Removed "awaiting translation" for french
Allow increasing the software PWM frequency.
Moved corexy implementation from stepper to planner
(Thanks iquizzle)
Merge branch 'deltabot' into Marlin_v1