Updated Pixel Service API (NeoPixel and DotStar)

[brentru]

Refactored the pixel service API to communicate with NeoPixel and DotStar LEDs.

• added ConfigurePixels C2D message which provides info about the type of pixel constructor to use, the pixel ordering, and the number of the pixels on a strip. Currently we only support NeoPixel and Dotstar, but this api should be extensible enough to add more.

• added PixelEvent C2D message which transmits pixel data (color, index of pixels to address). We can add parameters like brightness later.

[lorennorman]

Looks great. What does "C2D" mean?