Addresses issue #11 items unit testing, snapshot testing. Follows instructions from https://www.gatsbyjs.com/docs/how-to/testing/unit-testing/ ; Adding typescript config, mocks, snapshot capabilities; initial test for j40footer and snapshot, readme update, test helper for intl plugin (#79)

client/src/components/J40Footer.spec.tsx

@@ -0,0 +1,13 @@
+import React from 'react';
+import renderer from 'react-test-renderer';
+import J40Footer from './J40Footer';
+import {LocalizedComponent} from '../test/testHelpers';
+
+describe('J40Footer', () => {
+  it('renders correctly', () => {
+    const tree = renderer
+        .create(<LocalizedComponent><J40Footer /></LocalizedComponent>)
+        .toJSON();
+    expect(tree).toMatchSnapshot();
+  });
+});