Resolved few undo action on UI tabs - tabs were not getting activated

during undo-redo action. Also, resolved the focus losing issue, which
closing the subnode editor using undo action.

Also, resolved an issue related to 'beforeopen' failed on server node,
due to api changes on tree events.

web/pgadmin/static/js/backgrid/backgrid.pgadmin.js

@@ -139,6 +139,7 @@
 
       editorOptions['el'] = $(this.el);
       editorOptions['columns_length'] = this.column.collection.length;
+      editorOptions['el'].attr('tabindex' , 1);
 
       this.listenTo(this.model, "backgrid:edit", function (model, column, cell, editor) {
         if (column.get("name") == this.column.get("name"))
@@ -163,6 +164,8 @@
         this.$el.empty();
         this.$el.html("<i class='fa fa-pencil-square-o'></i>");
         this.delegateEvents();
+        if (this.grabFocus)
+          this.$el.focus();
         return this;
     },
     exitEditMode: function() {
@@ -173,6 +176,7 @@
       this.model.trigger(
           "pg-sub-node:closed", this, index
           );
+      this.grabFocus = true;
     },
     events: {
       'click': function(e) {