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.

Demos/Device/ClassDriver/KeyboardMouse/KeyboardMouse.h

@@ -46,7 +46,7 @@
 		#include <LUFA/Drivers/Board/LEDs.h>
 		#include <LUFA/Drivers/Board/Buttons.h>
 		#include <LUFA/Drivers/USB/USB.h>
-		#include <LUFA/Drivers/USB/Class/Device/HID.h>
+		#include <LUFA/Drivers/USB/Class/HID.h>
 
 	/* Macros: */
 		/** LED mask for the library LED driver, to indicate that the USB interface is not ready. */