Ported over Johann Rocholl's improvements for delta printers:

- Nonlinear auto bed leveling code (includes G29, G30, Z_RAISE_AFTER_PROBING). Cleaned it up to be a delta-specific AUTO_BED_LEVELING_GRID code path.
- Allen key z-probe deployment and retraction code. Cleaned it up and added safety checks.

Marlin/planner.cpp

@@ -1057,7 +1057,7 @@ Having the real displacement of the head, we can calculate the total movement le
   st_wake_up();
 }
 
-#ifdef ENABLE_AUTO_BED_LEVELING
+#if defined(ENABLE_AUTO_BED_LEVELING) && not defined(DELTA)
 vector_3 plan_get_position() {
 	vector_3 position = vector_3(st_get_position_mm(X_AXIS), st_get_position_mm(Y_AXIS), st_get_position_mm(Z_AXIS));