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.

Introduce save_delay() for long delays what otherwise would cause
watchdog resets

Explizit lcd_set_custom_characters(false) at the end of bootscreen().
Else the charset is not proper set in case of LCD_PROGRESS_BAR.

Init display and show bootscreen later, but init display in `kill()`
to init outputs before the bootscreen delays but being able to display
kill errors.

・Add more "UL" suffix
・Restore removed "UL" suffix

This is the easiest way to make button pin testing consistent without
renaming all the button pins. Just make a macro especially for testing
if button pins are set, since they are named consistently in the pins
files.

Fixed backlight for PCF8575.

Signed-off-by: Christian Inci <chris.pcguy.inci@gmail.com>

Following up on #3231

Alternative fix to #3149

lcd_erase_line() is called with argument, but the argument is ignored by lcd_erase_line().

Renamed `WARN_REDUCED_ACCURACY` to `DISABLE_REDUCED_ACCURACY_WARNING`

Changed the condition for blinking from
```
#if ENABLED(WARN_REDUCED_ACCURACY)
```
to
```
#if DISABLED(DISABLE_REDUCED_ACCURACY_WARNING)
```

Exactly the same - copy/paste.