Allows the user to send text to the serial console in order to
communicate with a host - sending debuging information or action
commands, for example.  Text must begin with '//' and this is added if
it is not already present at the beginning of the string.

Can't compile with PINS_DEBUGING enabled on Atmega1284p because it tries
to enumerate pins 46 and 47 (which don't exist) because `#ifdef
AVR_AT90USB1286_FAMILY ` doesn't work as expected.

Addressing #6992 and #5851

Use the raw position for mesh measurement. Otherwise the `M206` and
`M92` Z offsets will get canceled out by bed leveling. The downside is
`G29` will not compensate for a poorly set small `M206` fudge value.

To elaborate on this issue, imagine you are probing with a Z home
offset of -0.1, meaning when Z homes, -0.1 is the current position,
implying the ideal bed zero for the nozzle is 0.1mm higher than the Z
endstop. Ordinarily when printing, Z would raise 0.1mm higher.

What happens when we probe is that all points are measured with that
-0.1 included. So when bed leveling is enabled the `M206 Z` offset gets
exactly canceled out by the bed readings.

* Add Z Fade Height to M420 Output

Echo the z-fade height when M420 is called, if it is enabled.

* Fix Whitespace

* Fix Compiler complaint

* Missing semi-colon

Addressing #7057

================================

Changed to conditional compile for AT90USB issue

Original Mesh Bed Leveling replacement put at top of UBL Menu Options to
help facilitate the removal of the Original Mesh Bed Leveling.

Radar display (and control) of the UBL Interactive Mesh Editing.

Add support for the PCA9632 PWM color LED driver used on the Ultimaker 2 and Wanhao Duplicator 6.

* excentric probe config fix

* undo last commit

* eccentric probe fix

* oops

* !stow after each probe

* deploy/stow fix

* E parameter + bit of cleanup

* comment

* LCD menu fix

* Updates for ensure_safe_temperature

* M600 fixes

* [New Feature] I2C position encoder support

I plan to continue improving/cleaning this up, as there areas that need work.

* let the cleanups begin.

* progress

* more progress

* comments, rename files, etc.

* clean

* Cleanups per thinkyhead

* a few more cleanups

* cleanups, bugfixes, etc.

* remove unnecessary passes_test(), additional cleanups/optimizations

* cleanups

* misc.

* Fix up I2CPEM.init() and a few other things.

* organize, fix, rename, etc.

* more optimization

* a few more tweaks

Line 7830 prevented successfull compilation when #define CASE_LIGHT_ENABLE is uncommented