Add Wiimote and its core extensions

[whirvis]

Definitions for the Nintendo Wiimote (named Wiimote) should be created in the devices.wii module. Its core extensions should also be created. An accompanying adapter should be implemented in the hid-usb module.

The core extension of the Wiimote are defined as such:

Extension	Class
The Nunchuk	NunchukExtension
The Classic Controller	ClassicExtension
The Classic Pro Controller	ClassicProExtension
Wii Motion Plus	MotionPlusExtension

The ability for user to add support for their own extensions to Wiimote must be available.