Made launch wizard only accessible to owners

refs https://github.com/TryGhost/Team/issues/460

- member payment settings are only changeable by owners which would leave the wizard being a single step
- wizard is designed to be used as one of the first things after initial site setup which will be completed as the owner user

ghost/admin/app/controllers/dashboard.js

@@ -0,0 +1,6 @@
+import Controller from '@ember/controller';
+import {inject as service} from '@ember/service';
+
+export default class DashboardController extends Controller {
+    @service session;
+}

ghost/admin/app/routes/launch.js

@@ -1,3 +1,14 @@
 import AuthenticatedRoute from 'ghost-admin/routes/authenticated';
+import {inject as service} from '@ember/service';
 
-export default class LaunchRoute extends AuthenticatedRoute {}
+export default class LaunchRoute extends AuthenticatedRoute {
+    @service session;
+
+    beforeModel() {
+        return this.session.user.then((user) => {
+            if (!user.isOwner) {
+                return this.transitionTo('home');
+            }
+        });
+    }
+}

ghost/admin/app/templates/dashboard.hbs

@@ -6,6 +6,8 @@
     </GhCanvasHeader>
 
     <section class="view-container gh-main-width">
-        <LinkTo @route="launch">Launch site - Finish setup</LinkTo>
+        {{#if this.session.user.isOwner}}
+            <LinkTo @route="launch">Launch site - Finish setup</LinkTo>
+        {{/if}}
     </section>
 </section>