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/RNDISConstants.h

@@ -34,8 +34,8 @@
  *  constants, please refer to the Microsoft RNDIS specification.
  */
  
-#ifndef _RNDIS_CONSTANTS_H_
-#define _RNDIS_CONSTANTS_H_
+#ifndef _RNDIS_CONSTANTS_DEVICE_H_
+#define _RNDIS_CONSTANTS_DEVICE_H_
 
 	/* Macros: */
 		#define REMOTE_NDIS_PACKET_MSG                0x00000001UL