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/test/testHelpers.tsx

@@ -0,0 +1,16 @@
+import React, {ReactNode} from 'react';
+import {IntlContextProvider} from 'gatsby-plugin-intl';
+
+interface ILocalizedComponentProps {
+  children: ReactNode
+}
+
+export const LocalizedComponent = ({children}: ILocalizedComponentProps) => {
+  return (
+    <>
+      <IntlContextProvider value={{language: 'en', routed: true}}>
+        {children}
+      </IntlContextProvider>,
+    </>
+  );
+};