Move `led` module to `ws2812` module

[ajfisher]

Suggest moving the current LED module to being a specific ws2812 module and then breaking this up to have the basic functions (turning LEDs on and off etc) as part of this and then add a high order "drawing" module on top of it which can use it (or any other displayable method - eg an OLED, LED matrix or other device that can display pixel data).

[garthk]

aiko.neopixel perhaps? Not sure about the abstraction stack, but being able to distinguish between that and some tiny file we provide to control the LED on the back of the board would be nice.

[marcmerlin]

I'm ambivalent on this to be honest. I considered not using the aiko support at all, but figured I'd try so that it integrates with MQTT. I don't really need it, but i figured why not?
However, things are a bit harder than I planned, but you can have a look at what I've done so far: #32