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.
Custom Splash Screen for full graphic displays.
Too complicated for the hitachis without knowing what exactly to display.
On top of #4032
Realisation of an idea from #3996
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.
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)
```
Replaced displaying "---" instead of the value of a coordinate when
unhomed or with reduced precision
with blinking the coordinate-prefix-character ('X','Y','Z').
For "unhomed" a '?' is shown every second second - until that axis is
homed. The value displayed is, as before the "---" where displayed, the
relative to the reset position coordinate value.
When the axis stepper was disabled, now we can display a hint on that,
by showing a blinking ' ' instead of the axis letter, when
WARN_REDUCED_ACCURACY is defined.
I suppose the code itself is here the better documentation.
A '+/-' character is in non of our charsets so i decided for a '?' for
now to reduce the work.
There is no additional space on the displays one could use to display
the information, so replacing something is the only option. As the axis
letters are totally redundant with their positions on the display they
contain the least information.
So my decision was to overwrite them.
