Increase the ratio used to select an overview level from a bounding box

This value would ideally be adjusted to prevent the grid size of the
overview used being greater that one pixel. So, this should be the
larger dimension of the map window in pixels.

lib/cartodb/models/dataview/overviews/base.js

@@ -22,7 +22,8 @@ var SETTINGS = {
     defaultOverviews: false,
 
     // minimum ratio of bounding box size to grid size
-    zoomLevelFactor: 100.0
+    // (this would ideally be based on the viewport size in pixels)
+    zoomLevelFactor: 1024.0
 };
 
 // Compute zoom level so that the the resolution grid size of the