create visualization for pmf/categorical targets

[nickreich]

Per conversation with @lshandross and @elray1 , we discussed creating a standard visualization for (possibly step-ahead) categorical/pmf targets. I will post a white board picture when I get back to my office, but the idea would be to have x-axis as time (as with current predtimechart figures) y-axis as categories, colors as probabilities of each category, and some symbol to indicate observed categories.

[nickreich]

Adding whiteboard image...