added G666, online height adjustment during printing

Signed-off-by: FMMT666 <FMMT666@gmx.tm>
added G666, online height adjustment during printing

Signed-off-by: FMMT666 <FMMT666@gmx.tm>
added G666 (online height adjustment during printing) for LCD

Signed-off-by: FMMT666 <FMMT666@gmx.tm>
added G666, online height adjustment during printing
Added several useful commands to the LCD "Prepare" menu.
fixed some typos
added some text of recent changes
G666 works better with 0.1mm instead of 0.05
hit return once too often ;)
added a comment