conditionally hide load prior items button

fixes ADMIN-909

test plan:
- if there are past items to load, you should be able to tab to the
load prior items button
- if all past items are loaded, the load prior items button should be
missing.

Change-Id: Ibbe46802a26ae09419fe7c26e7861a586698e7e6
Reviewed-on: https://gerrit.instructure.com/147189
Tested-by: Jenkins
Reviewed-by: Mysti Sadler <mysti@instructure.com>
QA-Review: Deepeeca Soundarrajan <dsoundarrajan@instructure.com>
Product-Review: Jon Willesen <jonw+gerrit@instructure.com>

packages/canvas-planner/src/components/PlannerApp/__tests__/PlannerApp.spec.js

@@ -94,3 +94,13 @@ it('shows new activity button when there is new activity, but no current items',
     />);
   expect(wrapper.find('StickyButton')).toHaveLength(1);
 });
+
+it('shows load prior items button when there is more to load', () => {
+  const wrapper = shallow(<PlannerApp {...getDefaultValues()} />);
+  expect(wrapper.find('ShowOnFocusButton')).toHaveLength(1);
+});
+
+it('does not show load prior items button when all past items are loaded', () => {
+  const wrapper = shallow(<PlannerApp {...getDefaultValues()} allPastItemsLoaded />);
+  expect(wrapper.find('ShowOnFocusButton')).toHaveLength(0);
+});

packages/canvas-planner/src/components/PlannerApp/index.js

@@ -148,6 +148,7 @@ export class PlannerApp extends Component {
   }
 
   renderLoadPastButton () {
+    if (this.props.allPastItemsLoaded) return;
     return (
       <ShowOnFocusButton
         buttonProps={{