Clear the node cache, when an node is created/updated to make sure - we

will always have latest data related to that type of node. Also, fixed
the cache_level for different node types.

This commit also contains fixes for the following issue:
* In extension module - use the 'node-list-by-name' instead of using a
  custom 'node-ajax-options' control, and removed redundant template
  schemas from it.
* When we tries to destroy the select2 object from
  Select2Cell/Select2Control while releasing the properties view,
  sometimes select2 can not find the instance related it for some
  unknown reason. Hence - before removing it we will check for manual
  instance existance using $.data('select2').
* When we traverse through the browser tree nodes very quickly, it tries
  to remove the object before it gets created completely, and results
  into an exception.
* Icon in the select2 drop down list was not visible due to some CSS
  issues.

Apart of that, we will generate two new browser events -
'pgadmin-node:created:<NODE-TYPE>', 'pgadmin-node:updated:<NODE-TYPE>'
whenever a new node is created, or an existing node will be updated.

web/pgadmin/static/js/backform.pgadmin.js

@@ -1993,13 +1993,15 @@
       // Refresh SQL Field to refresh the control lazily after it renders
       setTimeout(function() {
         self.refreshTextArea.apply(self);
-      }, 100);
+      }, 0);
 
       return self;
     },
 
     refreshTextArea: function() {
-      this.sqlCtrl.refresh();
+      if (this.sqlCtrl) {
+        this.sqlCtrl.refresh();
+      }
     },
 
     remove: function() {

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

@@ -450,7 +450,11 @@
       this.undelegateEvents();
 
       if (this.$select) {
-        this.$select.select2('destroy');
+        if ( this.$select.data('select2')) {
+          this.$select.select2('destroy');
+        }
+        delete this.$select;
+        this.$select = null;
       }
 
       this.$el.empty();
@@ -530,7 +534,9 @@
 
     remove: function() {
       this.$select.off('change', this.onSave);
-      this.$select.select2('destroy');
+      if (this.$select.data('select2')) {
+        this.$select.select2('destroy');
+      }
       this.$el.empty();
       Backgrid.SelectCell.prototype.remove.apply(this, arguments);
      }