Add the ability to turn off the display for power savings

[mkatzNU]

If the display is not being used it would be nice to turn off the display or at least the backlight in the interest of power savings. Especially if the unit is mounted in a way where the display cannot be seen or will not be used.

[nullvalue0]

I didn't even know if this would be possible so I did a little experimenting.. And there is a way to put the screen to sleep and turn it off.. However, due to ... reasons ... the command to turn the screen back on doesn't work on it's own (it requires a controller chip reset). But resetting the Wemos and/or a soft reboot does bring the screen back on. So, as long as you were ok with these limitations I could add it as a feature.

[mkatzNU]

As an option I don't see why we don't add it.

If the display is off, changing the ATDISP=ON could also force a prompted reset as could pushing the home button while the display is off.