Reference: #6804

- can be augmented in the future to enable for other leveling systems

Quite simple, but did not want to modify `G1` as the additional checking would slow it down.

Tested & working.

- fix broken `M421` due to less-than-careful optimization
- add HOME_AFTER_DEACTIVATE define to advanced config so not everyone has to rehome after steppers are deactivated
- misc. cleanups (remove unused label, unused variables)

 - Add crc16 utility function
 - Implement CRC16 for config store, remove old checksum, increment layout version
 - Move UBL mesh store/load to MarlinSettings; increment UBL_VERSION
 - Begin to lay out MAT structure, prototype functions, etc.
 - Rename ubl.state.eeprom_storage_slot to .storage_slot
 - Misc. optimization
 - Cleanup/standardize/improve some messages

This is a work in progress!

Also clean up ubl_motion.cpp debug info and fix declaration of cx & cy

Extra closing curly bracket terminates while loop early if PRINTER_EVENT_LEDS defined

UBL on Delta's....     Should be close!    Should not affect any Cartesian printer.

- Split M421 into separate versions for bilinear and ubl
- Fix minor issue in G26

* M421 Mesh Point Offset and misc. UBL clean up

Allow M421 to accept an offset as well as absolute value for a specified
mesh point.
And misc. UBL clean up to reduce redundent code.

* Better error checking for M421

* Fix M421 Y index bug

I just noticed....  We've had a Y index bug for who knows how long?

Saves a few lines of code.

* Restore LSF functionality

Some of the typo's persisted...   Hopefully this gets them all fixed.

* Restore user's expectations of how G28 should behave

* Allow Nozzle size control with ornery host programs

 - rename to PROBING_HEATERS_OFF
 - move heater pausing functionality into thermalManager
   - add variables, pause(), ispaused(), other functions
 - add fan pausing functionality -> PROBING_FANS_OFF
 - add probing_pause() wrapper
 - move pausing into do_homing_move() and do_probe_move() to minimize quiet time and so other probe types can benefit
 - example configs

UBL Clean up.

also removed wayward 'address of' ampersand in setTargetHotend and setTargetBed parameters

When both lowering and recovery are performed using the same "prepare_move_to_destination()" the extruder recovery feedrate ends up being ignored and, instead, is only capped by either the maximum e-speed or the time it takes to perform the z-lowering. 
Performing the two moves separately from each other ensures a correct recovery feedrate.