Change appearance of centroid labels of unselected values (#1491)

* add opacity change on selection state

* change overlay z-index to capture pointer

* https://www.youtube.com/watch?v=xrg-RgF5F8o

* render null if no coloring by continuous

* run lint on push + pr

* revert commit

wrong branch

client/src/components/graph/overlays/graphOverlayLayer.js

@@ -81,7 +81,7 @@ export default class GraphOverlayLayer extends PureComponent {
           position: "absolute",
           top: 0,
           left: 0,
-          zIndex: 1,
+          zIndex: 2,
           backgroundColor: displaying ? "rgba(255, 255, 255, 0.55)" : "",
         }}
         onMouseMove={handleCanvasEvent}