Draft of changes to add color/scale to grids.

Okay, I am not sure whether this pull request will be correct now. If it has a lot of PenColor stuff, it's the previous one which was buggy. If it has a samples/grid/grid-color-scale, it's legit.

This is an update which adds the ability to specify RGBA color and scale per-item in grids. I am not sure whether I caught all the loose ends. It does not handle serializing. It's intended to be used for the Miracle Modus app, where I do a lot of things with large grids of squares, and they're painfully slow right now in Corona, and also painfully slow in Moai if I write the vertex buffers myself, computing them in Lua. Adding the color option seems to produce the results I want.