Single/Multiple colors everywhere in Style/Traces

Right now we have the nice single/multiple color selector just in marker.color. We want to be able to use the scale-picker basically everywhere that color can appear in 'multiple trace' contexts, like in 'fill' or 'border color' or whatever.

Note that we don't want to do this in the "multiple axes" context e.g. when "all" axes are selected and we're coloring e.g. the gridlines.