SDCARDDETECT -> SD_DETECT, added docs

- `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`

Marlin/example_configurations/delta/generic/Configuration.h

@@ -789,7 +789,7 @@ const bool Z_PROBE_ENDSTOP_INVERTING = true; // set to true to invert the logic
 //
 // ==> REMEMBER TO INSTALL U8glib to your ARDUINO library folder: http://code.google.com/p/u8glib/wiki/u8glib
 //#define ELB_FULL_GRAPHIC_CONTROLLER
-//#define SDCARDDETECTINVERTED
+//#define SD_DETECT_INVERTED
 
 // The RepRapDiscount Smart Controller (white PCB)
 // http://reprap.org/wiki/RepRapDiscount_Smart_Controller

Marlin/example_configurations/delta/generic/Configuration_adv.h

@@ -300,11 +300,12 @@
 
 #if ENABLED(SDSUPPORT)
 
-  // If you are using a RAMPS board or cheap E-bay purchased boards that do not detect when an SD card is inserted
-  // You can get round this by connecting a push button or single throw switch to the pin defined as SDCARDCARDDETECT
-  // in the pins.h file.  When using a push button pulling the pin to ground this will need inverted.  This setting should
-  // be commented out otherwise
-  #define SDCARDDETECTINVERTED
+  // Some RAMPS and other boards don't detect when an SD card is inserted. You can work
+  // around this by connecting a push button or single throw switch to the pin defined
+  // as SD_DETECT_PIN in your board's pins definitions.
+  // This setting should be disabled unless you are using a push button, pulling the pin to ground.
+  // Note: This is always disabled for ULTIPANEL (except ELB_FULL_GRAPHIC_CONTROLLER).
+  #define SD_DETECT_INVERTED
 
   #define SD_FINISHED_STEPPERRELEASE true  //if sd support and the file is finished: disable steppers?
   #define SD_FINISHED_RELEASECOMMAND "M84 X Y Z E" // You might want to keep the z enabled so your bed stays in place.