meta: introduce Cypress end-to-end testing (via #4827)

* `test/e2e` -> `test/e2e-selenium`

* add Cypress

* ESLint fixes

* MOAR cypress

* `integration` -> `tests`

* wire Cypress up to a hot e2e server

* linter fixes

* don't run in CI

test/e2e-selenium/scenarios/refs.js

@@ -0,0 +1,26 @@
+describe("Remote $ref rendering", function () {
+  let mainPage
+  beforeEach(function (client, done) {
+
+    mainPage = client
+    // expand the models so we don't have to manually do it
+    .url("localhost:3230?defaultModelsExpandDepth=5")
+    .page.main()
+
+    client.waitForElementVisible(".download-url-input:not([disabled])", 5000)
+    .pause(2000)
+    .clearValue(".download-url-input")
+    .setValue(".download-url-input", "http://localhost:3230/test-specs/refs/api1.yaml")
+    .click("button.download-url-button")
+    .pause(1000)
+
+
+    done()
+  })
+
+  it("renders a remote $ref correctly", function (client) {
+    mainPage.expect.element("#model-TestResponse > span > div > span > span > span.inner-object > table > tbody > tr:nth-child(2) > td:nth-child(2) > span > span > div > div > p").text.to.equal("this is an api2prop")
+
+    client.end()
+  })
+})