Make folder controls update sticky JS on change

Also removes a call the `render` method which
duplicates one already made by the
`selectActionButtons` method on load.

app/assets/javascripts/stick-to-window-when-scrolling.js

@@ -12,7 +12,6 @@
     this._appliedClass = null;
     this._$shim = null;
     this._stopped = false;
-    this.scrolledFrom = this._sticky.getScrolledFrom($el);
   };
   StickyElement.prototype.stickyClass = function () {
     return (this._sticky._initialPositionsSet) ? this._fixedClass : this._initialFixedClass;
@@ -106,9 +105,15 @@
   };
   Sticky.prototype.setElementDimensions = function (el, callback) {
     var self = this;
+    var $el = el.$fixedEl;
     var onHeightSet = function () {
       el.scrolledTo = self.getScrollingTo(el);
-      el.updateShim(el);
+      // if element is shim'ed, pass changes in dimension on to the shim
+      if (el._$shim) {
+        el.updateShim();
+        $el = el._$shim;
+      }
+      el.scrolledFrom = self.getScrolledFrom($el);
       if (callback !== undefined) {
         callback();
       }

app/assets/javascripts/templateFolderForm.js

@@ -36,8 +36,6 @@
 
       this.$form.on('click', 'button.button-secondary', (event) => this.actionButtonClicked(event));
       this.$form.on('change', 'input[type=checkbox]', () => this.templateFolderCheckboxChanged());
-
-      this.render();
     };
 
     this.addCancelButton = function(state) {
@@ -96,6 +94,11 @@
       this.states.forEach(
         state => (state.key === this.currentState ? this.$stickyBottom.append(state.$el) : state.$el.detach())
       );
+
+      // make sticky JS recalculate its cache of the element's position
+      if ('stickAtBottomWhenScrolling' in GOVUK) {
+        GOVUK.stickAtBottomWhenScrolling.recalculate();
+      }
     };
 
     this.nothingSelectedButtons = `