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

.github/workflows/e2e.yml

@@ -0,0 +1,13 @@
+name: example-cron
+on:
+  schedule:
+    # runs tests every day at 12am ET (4am UTC)
+    - cron: '0 4 * * *'
+jobs:
+  nightly:
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Cypress nightly tests 🌃
+        uses: cypress-io/github-action@v2