Integrate proptypes for our shared components.

- Fix unit tests.
- Fix linter errors.

__tests__/components/About.test.jsx

@@ -6,11 +6,11 @@ import About from '../../src/components/About';
 describe('<About />', () => {
   let aboutWrapper;
   let closeButton;
-
+  const onClose = jest.fn();
   test('initially renders without crashing', () => {
     aboutWrapper = mount(
       <I18nProvider>
-        <About isOpen />
+        <About isOpen onClose={onClose} />
       </I18nProvider>
     );
     expect(aboutWrapper.length).toBe(1);
@@ -18,7 +18,6 @@ describe('<About />', () => {
   });
 
   test('close button calls onClose handler', () => {
-    const onClose = jest.fn();
     aboutWrapper = mount(
       <I18nProvider>
         <About isOpen onClose={onClose} />