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.

・Add missing ')'

・Update forgotten example configurations

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.

Makr the call of   `manage_manual_move() ` depandent of `ULTIPANEL`

- `per_sq_second` => `per_s2`
- `per_sqr_second` => `per_s2`
- `axis_steps_per_sqr_second` => `max_acceleration_steps_per_s2`

This is an update of MarlinDev PR #196.

G20/21: support for switching input units between millimeters and
inches.
M149: support for changing input temperature units.

In support of these changes, code_value() and code_value_short() are
replaced with an array of functions which handle converting to the
proper types and/or units.