add de facto clean up of gl and geo container in Plots.purge:

- this makes Plotly.newPlot not pile up scenes and geos

Author: etpinard

shelly/plotlyjs/static/plotlyjs/src/graph_obj.js

@@ -1908,6 +1908,12 @@ plots.purge = function(gd) {
     // note: we DO NOT remove _context because it doesn't change when we insert
     // a new plot, and may have been set outside of our scope.
 
+    // clean up the gl and geo containers
+    // TODO unify subplot creation/update with d3.selection.order
+    // and/or subplot ids
+    gd._fullLayout._glcontainer.remove();
+    gd._fullLayout._geocontainer.remove();
+
     // data and layout
     delete gd.data;
     delete gd.layout;
@@ -1919,6 +1925,7 @@ plots.purge = function(gd) {
 
     delete gd.fid;
 
+
     delete gd.undoqueue; // action queue
     delete gd.undonum;
     delete gd.autoplay; // are we doing an action that doesn't go in undo queue?