Revert "fix: remove duplicate import and no relative import (#4015)"

This reverts commit 3ce9b50.

app/initializers/extensions.js

@@ -1,4 +1,4 @@
-import 'open-event-frontend/extensions/ember-table/component';
+import '../extensions/ember-table/component';
 
 export function initialize() {}
 

app/services/current-user.js

@@ -1,4 +1,5 @@
-import Service, { inject as service } from '@ember/service';
+import Service from '@ember/service';
+import { inject as service } from '@ember/service';
 import { isEmpty } from '@ember/utils';
 import { resolve } from 'rsvp';
 

app/services/device.js

@@ -1,9 +1,10 @@
 import $ from 'jquery';
-import Service, { inject as service } from '@ember/service';
+import Service from '@ember/service';
 import { computed } from '@ember/object';
 import { equal, or } from '@ember/object/computed';
 import { debounce } from '@ember/runloop';
 import { forOwn } from 'lodash-es';
+import { inject as service } from '@ember/service';
 
 /**
  * Keeping this outside the service object to keep it lean and faster to loop over

tests/test-helper.js

@@ -1,6 +1,6 @@
-import Application from './app';
+import Application from '../app';
 import QUnit from 'qunit';
-import config from 'open-event-frontend/config/environment';
+import config from '../config/environment';
 import { setApplication } from '@ember/test-helpers';
 import { start } from 'ember-qunit';
 import loadEmberExam from 'ember-exam/test-support/load';