Move out many of the common class driver constants into grouped enums, to make them more managable.

Add new CDC descriptor structs to the CDC class driver, so that the CDC demos can use human readable field names.

Rename prefix for Still Image Host class driver functions from "SImage_" to "SI_" to remain consistent with the rest of the driver.

Demos/Host/ClassDriver/KeyboardHost/KeyboardHost.c

@@ -50,7 +50,7 @@ USB_ClassInfo_HID_Host_t Keyboard_HID_Interface =
 				.DataOUTPipeNumber      = 2,
 				.DataOUTPipeDoubleBank  = false,
 				
-				.HIDInterfaceProtocol   = HID_BOOT_KEYBOARD_PROTOCOL,
+				.HIDInterfaceProtocol   = HID_BOOTP_KeyboardBootProtocol,
 			},
 	};