* UBL G29 -P3.1 mesh fill with distance-weighted least squares fit.

* Back to original -O0 on G29 for now.

* Misc. Clean Up

Mostly UBL related clean up.
- But fixed a bug in the thermistortables.
- Made G26 more responsive to user aborts.
- Added sanity checks for older name for UBL_MESH_VALIDATION.
- Made G29 P4 able to edit invalidated mesh points
- Restore a reasonable Fade Height for UBL when creating new state information
- Get UBL's Topology Map to look a little bit better
- Make sure the user doesn't see a blank screen when doing Mesh Editing.

* Huh???   GitHub Desktop screwed up!

* get the planner object in scope

* Fix out of scope z_fade_height

* Travis timed out...

I need a change so I can force a new commit and sync.

Reference: #6804

Plus some other UBL tweaks.

- 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!

* Fix M48 for Delta's  There was a scope issue: DELTA_PROBEABLE_RADIUS wasn't getting defined.

* Check if the specified G29 command requires homing

Things should be pretty stable for a while.   
But it wouldn't surprise me if the Delta people have a need for a few special commands.

Since we already used 'T' for `G29` Topology Report in the past, and since 'T' is available…

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

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

- allow H code value to override probing height
- minor cleanups

- 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?

    /**
     * UBL System submenu
     *
     *  Prepare
     * - Unified Bed Leveling
     *   - Activate UBL
     *   - Deactivate UBL
     *   - Mesh Storage
     *       Memory Slot:
     *       Load Bed Mesh
     *       Save Bed Mesh
     *   - Output Map
     *       Map Type:
     *       Output Bed Mesh Host / Output Bed Mesh CSV
     *   - UBL Tools
     *     - Build Mesh
     *         Build PLA Mesh
     *         Build ABS Mesh
     *       - Build Custom Mesh
     *           Hotend Temp:
     *           Bed Temp:
     *           Build Custom Mesh
     *         Info Screen
     *       - Build Cold Mesh
     *       - Fill-in Mesh
     *           Fill-in Mesh
     *           Smart Fill-in
     *           Manual Fill-in
     *           Info Screen
     *         Continue Bed Mesh
     *         Invalidate All
     *         Invalidate Closest
     *     - Validate Mesh
     *         PLA Mesh Validation
     *         ABS Mesh Validation
     *       - Custom Mesh Validation
     *           Hotend Temp:
     *           Bed Temp:
     *           Validate Mesh
     *         Info Screen
     *     - Edit Mesh
     *         Fine Tune All
     *         Fine Tune Closest
     *       - Adjust Mesh Height
     *           Height Amount:
     *           Adjust Mesh Height
     *         Info Screen
     *     - Mesh Leveling
     *         3-Point Mesh Leveling
     *       - Grid Mesh Leveling
     *           Side points:
     *           Level Mesh
     *         Info Screen
     *   - Output UBL Info
     */

UBL Clean up.

add BLTouch-related messages in english and (rusty) french;
add missing endstops.h in ultralcd.cpp;
fix misc. compiler warnings;
fix lsf_reset - ZERO macro can't handle a pointer as it would only memset the size of the pointer, not the size of the entire struct