Add SDEXTRASLOW which runs the SD card at SPI_QUARTER_SPEED. Quarter speed is needed for RIGIDBOT_PANEL

As noted in #130 allen key probe stow rate is based on homing rates,
but homing rates were left out of most delta configs. This unifies the
XYZ homing rates and applies the unified rates to allen key movements.

As noted by @o-lampe at https://github.com/MarlinFirmware/MarlinDev/issues/114#issuecomment-136757614 the `MANUAL_FEEDRATE` for Delta Z should be the same as XY.

* Re-bump speed divisor should be the same for delta printer.

With the introduction of the #if ENABLED(…)

reads better than

* Updates the auto bed leveling comments ONLY.
* Renames "Z probe" word usage in //comments and #errors properly.

* Fix a couple of renames omission and macro expansion errors.

Currently we use the probe exclusively as a device to find the build platform(bed).
For the currently supported setups this means, we use it as a additional min-endstop.
A triggered when not deployed probe disturbs the homing process for max-endstops.

Rename ENDSTOPPULLUP_ZPROBE to ENDSTOPPULLUP_ZMIN_PROBE
Rename Z_PROBE_ENDSTOP_INVERTING to Z_MIN_PROBE_ENDSTOP_INVERTING
Rename Z_PROBE_ENDSTOP to Z_MIN_PROBE_ENDSTOP
Rename DISABLE_Z_PROBE_ENDSTOP to DISABLE_Z_MIN_PROBE_ENDSTOP
Rename Z_PROBE_REPEATABILITY_TEST to Z_MIN_PROBE_REPEATABILITY_TEST
Rename Z_PROBE_ENDSTOP to Z_MIN_PROBE_ENDSTOP
Adjust comments accordingly
Remove Z_MAX  check for the probe in update_endstops().

Using an delta related idea of @clefranc from #61,
extended to the general change for all setups.

Tested with Prusa i3, max-z-endstop and permanently triggered z-probe.
Worked for @clefranc's delta.

The long descriptor will still be available in M115

- For some reason it’s easy to forget what BT stands for, but it
doesn’t need an abbreviation.

- The default serial baud rate of 115200
- The regular RigitBot bed size 254mm/248mm/254mm
- Single stock extruder
- Stock termistors for extruder and hotbed
- Stock Min X/Y/Z stops. Max stops not connected
- Stock 32 teth tooleys (stock axis steps)
- No auto bed leveling
- No screen

- `SD_DETECT_PIN` replaces `SDCARDDETECT`
- `SD_DETECT_INVERTED` replaces `SDCARDDETECTINVERTED`
- Revise the description of `SD_DETECT_INVERTED`
- Add a note about the override of `SD_DETECT_INVERTED` in
`Conditionals.h`

As suggested in #2521
- Move `ABORT_ON_ENDSTOP_HIT_FEATURE_ENABLED` because `SDSUPPORT` is
also required.
- Add a note that endstops must be enabled for the feature to have any
effect

A speaker needs a AC or a pulsed DC to make a sound, a buzzer only needs a DC.
A buzzer has it's own resonator. It works in most cases to feed the buzzer with a pulsed DC, but the sound will not be as loud as with pure DC.

There seem to be boards where the BEEPER-pin is not able to handle a PWM. Obviously intended for a buzzer.
To make these board able to handle a speaker

* replace the PWM based tone()-function again with a on-delay-off-delay loop.

Hopefully the last time I touch the beeper code.

Just set up the pin. Don't move to a random position.

Simplify servo::move()
* servo::move() does not need the pin parameter - The pin is set during servo_init() with attach().
* servo::move() does not need a return value.

SERVO_LEVELING is the wrong condition to deactivate the servos.

Remove some temporary (Servo *) variables.
SanityCheck for the servo indexes.