refactor(toolbar): allow any content in the center

ionic/components/tabs/test/basic/index.ts

@@ -99,12 +99,16 @@ class Tab3 {}
       </ion-content>
     </ion-menu>
 
-    <ion-tabs #content tabbar-style="secondary">
+    <ion-tabs #content>
       <ion-tab tab-title="Plain List" tab-icon="star" [root]="root1"></ion-tab>
       <ion-tab tab-title="Schedule" tab-icon="globe" [root]="root2"></ion-tab>
       <ion-tab tab-title="Stopwatch" tab-icon="stopwatch" [root]="root3"></ion-tab>
     </ion-tabs>
-  `
+  `,
+  config: {
+    navbarStyle: 'secondary',
+    tabbarStyle: 'secondary'
+  }
 })
 export class TabsPage {
   constructor() {