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/Keyboard/Keyboard.h

@@ -52,7 +52,7 @@
 		#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>
 
 	/* Type Defines: */
 		/** Type define for the keyboard HID report structure, for creating and sending HID reports to the host PC.