USBCON is definied by serial.h pullikng in MarlinConfig.h which in turn pulls in Arduino.h.  Defining in later includes has shown to cause compile issues so removing all extraneous calls for and potentially easier future linker troubleshooting.
more USBCON unification

Connected as described at http://printrbot.com/shop/led-strip/

Based on patch by Kelly Anderson <kelly@xilka.com> at
http://www.xilka.com/printrbot/marlin/1.1.4/20170707/

Signed-off-by: Alexey Shvetsov <alexxy@gentoo.org>

This allows the use of D4 as PS_ON since MKS Gen doesn't have a PS_ON pin. However this effectively allows only 3 servos (instead of 4).

Signed-off-by: Alexey Shvetsov <alexxy@gentoo.org>

Add more details as requested in #7198

Without this...  The LSF won't work because none of the sampled points
in this code block get added.

This was broken by 9af67e2446.

We can save more and a pile of RAM by eleminating the eqnBVector and
EqnAMatrix arrays next.

When a user executes a User Menu command, the LCD returns to the main menu. If the user has multiple menu items they want to run, such as one menu item per bed leveling corner, then it's better to stay in the User Menu rather than return to the main menu.

This PR modifies Marlin to stay in the User Menu after a command.

Fix compile error when UBL is enabled but there is no LCD Panel.

20x4 map integration.    Also some minor changes to the UBL Menu layout.     Both 20x4 LCD's and Graphical LCD panels should have similar functionality now.

Creality board is a Melzi / Sanguinololu variant, but using different pins for LCD control (and maybe other minor variations)

Fixes #7250

Addressing #7227

DISABLE_[XYZ] is incompatible with HOME_AFTER_DEACTIVATE and Z_SAFE_HOMING

Sends pre-defined string as action command when printer is kill.

Probing with the effector in the printing area, but an eccentric probe (e.g. allen key) outside it but still touching the bed gives meaninfull information for calibration. Since calibration is most accurate when probing as close to the towers as possible the testing was way to restrictive hence this fix.