Z-order of plots inconsistent with creation order

[bjkomer]

The z-order of plots (which one appears on top) seems to be dependent on the alphabetical ordering of the number assigned to them in the config. e.g. [_viz_2] will appear on top of [_viz_1] but [_viz_2] will also appear on top of [_viz_11].

Some consistent way of choosing which plot is on top is helpful when some displays have an opaque background and you want to put a transparent background plot on top of it.