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add test to Travis

 - 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!

The first character in the string wasn't blanked if the number went from >= 100 to <100, resulting in artefacts in the displayed string.

Also...   The memory corruption issue may be fixed.   The GCC compiler
was inlining static functions and this caused the G29() stack frame to
become much larger than the AVR could handle.

The `ftostr4sign` function got munged by the `WITHIN` patch

`ftostr62sign()` is used only when displaing/editing
Steps/mm. A sign is not needed - the value is always positive.
Because the number part is long there is no't much place for the values name.
With this PR the is one more char for the name possible.

And reduce the function size to simplify

_123, -123, _-12, __-1  plus  1234, 12.3, -1.2

- This function becomes obsolete if ftostr4sign is re-written.

・Fix memory leak

Includes:
  *firmware version / branch / date.
  *extruder count
  *board information (name, serial details, power supply type)
  *thermistors (names, min/max temperatures)
  *printer statistics (PRINTCOUNTER details)

Thanks to @thinkyhead for contributions.

Following up on #3231

Hopefully this is helpful to organization and future expansion….

Hopefully this is helpful to organization and future expansion….

Hopefully this is helpful to organization and future expansion….