This is an update of MarlinDev PR #196.

G20/21: support for switching input units between millimeters and
inches.
M149: support for changing input temperature units.

In support of these changes, code_value() and code_value_short() are
replaced with an array of functions which handle converting to the
proper types and/or units.

Fix for PR #3526(Configuration.h LCD & SDCard section rewrite)

It removes duplicated BQ_LCD_SMART_CONTROLLER.

The `Z_SAFE_HOMING` feature is coupled with probes and not leveling, so
make it available for general use.

Following up on #3231

Fixes for #3189

Setting a temp is still missing