Add host mode USB Class driver stubs, add beginnings of a CDC host class driver.

Split out common defines/types from class drivers into a seperate common class driver directory.

Make central USB Class driver dispatch headers, used for both device and host modes.

LUFA/Drivers/USB/Class/Device/CDC.c

@@ -28,7 +28,10 @@
   this software.
 */
 
-#define  INCLUDE_FROM_CDC_CLASS_C
+#include "../../HighLevel/USBMode.h"
+#if defined(USB_CAN_BE_DEVICE)
+
+#define  INCLUDE_FROM_CDC_CLASS_DEVICE_C
 #include "CDC.h"
 
 void CDC_Device_Event_Stub(void)
@@ -195,3 +198,5 @@ void CDC_Device_SendControlLineStateChange(USB_ClassInfo_CDC_t* CDCInterfaceInfo
 	Endpoint_Write_Stream_LE(&LineStateMask, sizeof(LineStateMask), NO_STREAM_CALLBACK);
 	Endpoint_ClearIN();
 }
+
+#endif