Addressing #3325 – Avoid undefined symbol errors in the compiler.

Redo of #3268 by @jbrazio

Following up on #3231

documentation/LCDLanguageFont.md moved to http://www.marlinfirmware.org/ at commit 12d0983757,
but http://www.marlinfirmware.org/ isn't working.

If Marlin is blocking the serial input or command queue for any length
of time (for example more than 2 seconds), it needs to send a message
to serial out to inform the host that it is busy. Marlin should only
send these messages out when busy, and preferably not when trying to
print formatted output.

Addressing #2879. The M115 report should display `MACHINE_UUID` but it
always displays `UUID`.

- Defining `SOURCE_CODE_URL` in `Default_Version.h` overrides it
elsewhere. So don’t define it there.
- Also fix up `language.h` so no `#undef` will be needed.

This is a proposed change. This section of M114 output is a debug
extension according to RepRap wiki.

Keep "astyled" reformatting

Added comment for Czech language (associated with file language_cz.h).

The long descriptor will still be available in M115

Apply `ENABLED` / `DISABLED` macros to language-related files.

and translate them to German.

Now send only temperature for T or B, but not send OK.
Host interprets the line to show the right temperature, but not in
response to M105 then stop and send commands until it ends the autotune.

- Use `setTargetedHotend` in `M200`, as with other commands that use
`T` for the extruder
- Synthesize the "invalid extruder" message, obviating several long
strings

language.h: update documentation for LANGUAGE_INCLUDE

@thinkyhead What do you think? I think there should be a warning like
this.

Now ending in an endless loop.
Tidy up the output format.
We now get:
ERRORTEXT ", system stopped! Heater_ID: " HEATERID

Where ERRORTEXT can be:
"Heating failed"
"Thermal Runaway"
"MAXTEMP triggered"
"MINTEMP triggered"
and soon
"Thermal Jump"

HEATERID can be
0, 1, 2 ,3 , "bed"

This messages are always followed by the common:
"Printer stopped due to errors. Fix the error and use M999 to restart. (Temperature is reset. Set it after restarting)"

This reverts the changes done to the error message for line number mismatches done in commit d43cc2dd5f

- Also move audio feedback into the command
- Added shorthand for `lcd_buzz` availability

This makes `M421` more amenable for irregular matrices

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

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

- Replace “Mendel” with “RepRap”

+ update in documentation

Thank you @Nprod!