Adding Cypress for e2e testing (#85)

* using the higher-level react-testing-library, and regenerating snapshot - renders real DOM elements
* Basic e2e testing with Cypress, following the guide here: https://www.gatsbyjs.com/docs/how-to/testing/end-to-end-testing/ ; needed to install cypress-local to avoid jest-cypress collision
* Adding accessibility testing support and basic a11y tests
* adding failure logging
* Adding nightly test run
* Fix misc stuff from lighthouse (#81)
* Removing local-cypress, relying instead on a combination
of type reference and eslint-plugin-cypress;
adding cypress to jest ignore paths to avoid conflict -
`npm test` is now jest-only, use `npm run test:e2e` to run cypress tests
* updating comment to clarify timezone

client/cypress/e2e/sample.spec.js

@@ -0,0 +1,11 @@
+// / <reference types="Cypress" />
+
+describe('Translation Test', () => {
+  it('Checks that locales have correct content', () => {
+    cy.visit('http://localhost:8000');
+    cy.url().should('include', '/en/');
+    cy.get('header').contains('Justice40');
+    cy.visit('http://localhost:8000/es');
+    cy.get('header').contains('Justicia40');
+  });
+});