This makes `M421` more amenable for irregular matrices

Updated "servo.h" to "Servo.h"

Corrected "servo.h" to "Servo.h" because of the updated filename.

- Add “Level Bed” menu item for auto bed leveling
- Hide the option if homing has not been done yet
- Arrange the Prepare submenu more logically (?)
- Add documentation comments, some white-space
- Apply some coding standards here and there
- Move old encoder multiplier debug option to `ultralcd.cpp`

language_de.h: updated translation and minor typos

language.h: update documentation for LANGUAGE_INCLUDE
language.h: URL für K8200 github repository

K8200 example Configuration.h:
* STRING_URL removed: like proposed by thinkyhead in #1917

This addresses comments in #1956 and #1079. In particular, this is useful
when both endstops are stationary on a CoreXY system, and the Y axis needs
to be homed before the X so the flags are aligned.

Edited the European part of 'ISO10646_CN.fon' to match the existing fonts.
Added Chinese font to make_fonts.bat
Created 'dogm_font_data_ISO10646_CN.h'
Added Chinese to 'language.h'
Added 'language_cn.h' with some minor edits.
Added Chinese font in 'language_en.h' to not fall back to European font.
Added cn to 'Configuration.h'
Changed WIDTH to LCD_PIXEL_WIDTH and HEIGHT to LCD_PIXEL_HEIGHT to have more descriptive names.

In 'dogm_lcd_implementation.h'
Added Chinese Font
Made 1 pixel more room for the larger Chinese font on the status line.
Changed geometry of the 'select bar' by one pixel.
Changed the way the position for values and postcars are set.

With these changes the output of `M503 S0` is all you need to restore
the EEPROM. Building on this it is straightforward to save and restore
the EEPROM state using the SD card or external GCode file.

- Added `M145` to set “heatup states” for the LCD menu
- Added `M420` to toggle Mesh Bed Leveling
- Added `M421` to set a single Mesh coordinate
- Extended `Config_PrintSettings` with added M codes
- Cleaned up some comments here and there

- Add `M111` as a standard option to set the debug level
- Implement `DEBUG_ECHO` in `process_commands`
- Other debug levels (e.g., `DEBUG_DRYRUN`) need more work

- Address issue raised in #1961

Else will throw error:
@:0 B@:0
Error:No thermistors - no temperature
[ERROR] Error:No thermistors - no temperature

when no bed is defined

delete some tabs

Ensure the probe offset will always be included when homing Z.

c'n'p ftw :/

and add some documentation - how to integrate a new font.

Syntax error.

no user will home to 0 with a max endstopp

and removed some tabs.

Centralised beep code to lcd_buzz().
From gcode_M300() and lcd_quick_feedback().

Enforced max. duration for M300 to 5 seconds.

Corrected description in 'Configuration.h'

LCD_FEEDBACK_FREQUENCY_HZ 0 gives now a silent delay of
LCD_FEEDBACK_FREQUENCY_DURATION_MS.

Corrected wrong order of parameters.