added e2e tests (#298)

- added e2e tests for
  - banner
  - history
  - intro
  - language
  - link
- added e2e workflow
- added cypress badge to README

cypress/integration/banner.spec.ts

@@ -0,0 +1,26 @@
+import { banner } from '../support/config'
+
+describe('Banner', () => {
+  beforeEach(() => {
+    cy.visit('/')
+    expect(localStorage.getItem('bannerTimeStamp')).to.be.null
+  })
+
+  it('shows the correct alert banner text', () => {
+    cy.get('.alert-primary.show')
+      .contains(banner.text)
+  })
+
+  it('can be dismissed', () => {
+    cy.get('.alert-primary.show')
+      .contains(banner.text)
+    cy.get('.alert-primary.show')
+      .find('.fa-times')
+      .click()
+      .then(() => {
+        expect(localStorage.getItem('bannerTimeStamp')).to.equal(banner.timestamp)
+      })
+    cy.get('.alert-primary.show')
+      .should('not.exist')
+  })
+})