Add symbolic names for USB Device String Descriptors within the demos, applications and bootloaders.

Bootloaders/CDC/Descriptors.h

@@ -127,6 +127,17 @@
 			USB_Descriptor_Endpoint_t                CDC_DataInEndpoint;
 		} USB_Descriptor_Configuration_t;
 
+		/** Enum for the device string descriptor IDs within the device. Each string descriptor should
+		 *  have a unique ID index associated with it, which can be used to refer to the string from
+		 *  other descriptors.
+		 */
+		enum StringDescriptors_t
+		{
+		    STRING_ID_Language      = 0, /**< Supported Languages string descriptor ID (must be zero) */
+		    STRING_ID_Manufacturer  = 1, /**< Manufacturer string ID */
+		    STRING_ID_Product       = 2, /**< Product string ID */
+		};
+
 	/* Function Prototypes: */
 		uint16_t CALLBACK_USB_GetDescriptor(const uint16_t wValue,
 		                                    const uint8_t wIndex,