Added default newsletters for new member via Admin

refs https://github.com/TryGhost/Team/issues/1469

- default newsletters were set for new members added on members list except "add yourself" feature
- updates default newsletters for new member added via "Add yourself" button

app/components/gh-members-no-members.js

@@ -17,10 +17,12 @@ export default class GhMembersNoMembersComponent extends Component {
     @task({drop: true})
     *addTask() {
         const user = yield this.session.user;
+        const defaultNewsletters = yield this.store.query('newsletter', {filter: 'status:active+subscribe_on_signup:true+visibility:members'});
 
         const member = this.store.createRecord('member', {
             email: user.get('email'),
-            name: user.get('name')
+            name: user.get('name'),
+            newsletters: defaultNewsletters
         });
 
         try {