UI - no jquery (#6768)

* add no-jquery rule and move event listeners to ember-concurrency tasks

* remove unnecessary onchange and handleKeyDown actions

* add element.closest polyfill and convert linked-block to use native dom apis

* update pretender, fetch, page-object, add optional-features, remove ember/jquery

* turn off jquery inclusion

* remove jQuery.isPlainObject usage

* violatedDirective isn't always formatted the same

* use fetch and the ember-fetch adapter mixin

* move to fetch and lowercase headers for pretender

* display non-ember-data errors

* use new async fn test style and lowercase headers in auth service test

* setContext is not necessary with the new style tests and ember-cli-page-object - it actually triggers jquery usage

* update ember-fetch, ember-cli-pretender

* wait for permissions check

* lowercase header name in auth test

* refactor transit tests to one test per key type

* simplify pollCluster helper

* stop flakey tests by prefering the native fetch

* avoid uncaught TransitionAborted error by navigating directly to unseal

* unset model on controller after unloading it because controllers are singletons

* update yarn.lock

ui/tests/integration/components/mount-backend-form-test.js

@@ -16,13 +16,11 @@ module('Integration | Component | mount backend form', function(hooks) {
   setupRenderingTest(hooks);
 
   hooks.beforeEach(function() {
-    component.setContext(this);
     this.owner.lookup('service:flash-messages').registerTypes(['success', 'danger']);
     this.server = apiStub();
   });
 
   hooks.afterEach(function() {
-    component.removeContext();
     this.server.shutdown();
   });