Move responsibility for scaling brightness to color correction/temperature into the controller objects.  Return scale to being a uint8_t
* Move brightness into a 8 bit scalar
* Move loop control into PixelController and update everything to use PixelController
* Replace writeBytes3 methods in the SPI implementations with writePixels instead, and have them use PixelControllers.
* Prototype using the DWT cycle counter for sam like k20 (doesn't work yet, however)
* Other minor code cleanups
Fix SPI builds