Prevent default drag and drop of background tile images if interaction handlers don't prevent dragging for some reason

css/80_app.css

@@ -3993,6 +3993,8 @@ img.tile {
     -ms-user-select: none;
     user-select: none;
 
+    -webkit-user-drag: none;
+
     opacity: 0;
 
     -webkit-transition: opacity 200ms linear;

modules/renderer/tile_layer.js

@@ -198,6 +198,7 @@ export function rendererTileLayer(context) {
         image.enter()
           .append('img')
             .attr('class', 'tile')
+            .attr('draggable', 'false')
             .style('width', _tileSize + 'px')
             .style('height', _tileSize + 'px')
             .attr('src', function(d) { return d[3]; })