Can't use "#define Z_MIN_PROBE_PIN Z_MAX_PIN" in configuration.h

Tweak serial macros

* Updates for ensure_safe_temperature

* M600 fixes

I recently upgraded my Marlin to V1.1.x and decided to publish my fix to make marlin compile properly when #define board megatronics 2 in combination with #define reprapworld keypad v1.1. It was previously described in the comments of a closed pull request. MarlinFirmware#472. All the buttons on the keypad are now operational.

* [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

Fix type for max_acceleration_mm_per_s2 in configuration_store.cpp

Add "static"

Fix for #6980 (case_light compile problem when EXTENDED_CAPABILITIES_REPORT is enabled)

There was quite a lot to translate this time. I'm not absolutely confident with the whole UBL stuff and it's a PITA to translate. I don't use any kind of levelling myself as i just have a perfectly level cast aluminium plate as bed.
So maybe someone who really uses it might take a closer look at it after it's merged.

Line 7830 prevented successfull compilation when #define CASE_LIGHT_ENABLE is uncommented

Use createChar_P to save SRAM in bootscreen

Enable AUTO_REPORT_TEMPERATURES by default

Leveling type in About Printer

...by moving `homing_feedrate_mm_s` to PROGMEM.

Fix z_endstop_adj initializer

Show the Leveling system in use on the About Printer screen.

Ref #5139

* Remove requirement for LCD when UBL is used.

* fix previous oversights

* further refinement - error messages for P2 & P4

* require R on G26 when not using LCD; default to all points