Surface the autodesk scatter plot animations in the standard deviation lesson

[flannery-denny]

This felt really disjointed in the scatter plots lesson and makes much more sense at the point at which students actually know what the computations on the right side of the animation mean, so I've moved to its own section in the standard deviation lesson on the alg2-split branch. But haven't fleshed out the section... and perhaps there's a simpler way to weave it in?