Merge pull request #1 from ErikZalm/Marlin_v1

merge
Activate LiquidTWI2 device detection and space-pad LCD status line.
Merge https://github.com/ErikZalm/Marlin into Marlin_v1
Prevent SD card insertion from causing a hang when using LiquidTWI2 device detection
Merge branch 'lcd_detected' of https://github.com/whosawhatsis/Marlin into Marlin_v1
Merge branch 'Marlin_v1' of https://github.com/ErikZalm/Marlin into Marlin_v1
Allow use of either SD Card slot when LCD Panel is configured.
Preference is for Controller SD slot before LCD Panel slot when both are occupied.
Merge branch 'Marlin_v1' of https://github.com/ErikZalm/Marlin into Marlin_v1
Merge branch 'Marlin_v1' of https://github.com/ErikZalm/Marlin into Marlin_v1
Merge branch 'Marlin_v1' of https://github.com/ErikZalm/Marlin into Marlin_v1
Support for Gen3 Monolithic electronics

Techzone Monotronics support, ignoring the tip manager and using fan connector as on Sprinter FW
TODO: Add support for tipmanager
Merge https://github.com/ErikZalm/Marlin into Marlin_v1
Merge branch 'Marlin_v1' of https://github.com/ErikZalm/Marlin into Marlin_v1
Implementation of FW extruder change retract

FW retraction is extended onto swap retraction invoked by 'G10 S1'.
Bookkeeping of the retract state of all extruders allows for having one
extruder fw standard retracted while another extruder is swap retracted.
An LCD menu item for the swap retract and recover length was added.
Merge branch 'Marlin_v1' of https://github.com/ErikZalm/Marlin into Marlin_v1
restore Branch from Backup

sorry for that
fixed wrong compiler-option
Fix lcd itostr3() to handle negative numbers
optimised some math-code
Merge branch 'Marlin_v1' of https://github.com/ErikZalm/Marlin into Marlin_v1