Added Config variables for activating I2C LCDs and setting type and address

Marlin/Configuration.h

 // The RepRapDiscount Smart Controller (white PCB)
 // http://reprap.org/wiki/RepRapDiscount_Smart_Controller
 //#define REPRAP_DISCOUNT_SMART_CONTROLLER
-
+
-// The GADGETS3D G3D LCD/SD Controller (blue PCB)
+// The GADGETS3D G3D LCD/SD Controller (blue PCB)
-// http://reprap.org/wiki/RAMPS_1.3/1.4_GADGETS3D_Shield_with_Panel
+// http://reprap.org/wiki/RAMPS_1.3/1.4_GADGETS3D_Shield_with_Panel
 //#define G3D_PANEL
 
 //automatic expansion
   #endif
 #endif
 
+//The LCD is attached via an I2C port expander.
+//#define LCD_I2C
+#ifdef LCD_I2C
+  // Port Expander Type - PCF8574 or MCP23008
+  #define LCD_I2C_TYPE PCF8574
+  // I2C Address of the port expander
+  #define LCD_I2C_ADDRESS 0x20
+#endif
+
 // Increase the FAN pwm frequency. Removes the PWM noise but increases heating in the FET/Arduino
 //#define FAST_PWM_FAN