Fix switch between modes and scrolling on adjust

The templateFolderForm JS was setting the mode to
'dialog' but not back when the state was changed
back to a normal sticky element. This caused
adjustments and scrolling when no adjustment
needed to be accommodated.

There were also problems with adjustForResize. It
was manipulating the same flag that resizing the
window did and returned a value never used.

app/assets/javascripts/templateFolderForm.js

@@ -139,6 +139,8 @@
     };
 
     this.render = function() {
+      var mode = 'default';
+
       // detach everything, unless they are the currentState
       this.states.forEach(
         state => (state.key === this.currentState ? this.$stickyBottom.append(state.$el) : state.$el.detach())
@@ -146,8 +148,9 @@
 
       // use dialog mode for states which contain more than one form control
       if (['move-to-existing-folder', 'add-new-template'].includes(this.currentState)) {
-        GOVUK.stickAtBottomWhenScrolling.setMode('dialog');
+        mode = 'dialog';
       }
+      GOVUK.stickAtBottomWhenScrolling.setMode(mode);
       // make sticky JS recalculate its cache of the element's position
       GOVUK.stickAtBottomWhenScrolling.recalculate();
     };