add handler for 'nameOverride' field in pointData

- similar to 'extraText', to allow trace modules' hoverPoints
  methods to override the 'name' hover label content.

Author: etpinard

src/plots/cartesian/graph_interact.js

@@ -974,6 +974,8 @@ function createHoverText(hoverData, opts) {
             contrastColor = tinycolor(traceColor).getBrightness() > 128 ?
                 '#000' : Color.background;
 
+        // to get custom 'name' labels pass cleanPoint
+        if(d.nameOverride !== undefined) d.name = d.nameOverride;
 
         if(d.name && d.zLabelVal === undefined) {
             // strip out our pseudo-html elements from d.name (if it exists at all)