Tabs template should set <tabName>Root with page class reference instead of page name string

Now the template is like below.

```typescript
export class TabsPage {

tab1Root = 'Tab1Page' // Look here
tab2Root = 'Tab2Page'
tab3Root = 'Tab3Page'

constructor(public navCtrl: NavController) { }

}
```

This causes url problem on desktop browser. When the first tab is selected, the url will be changed to something like `http://localhost:8101/#/tab1`. I spend hours to find out the solution: change `'Tab1Page'` to `Tab1Page` and import the class.

Locate the generated TabsPage template and inspect the tab1Root, tab2Root, and tab3Root values shown in the issue. Generate a tabs app and check the first tab in a desktop browser; done means the template uses the imported page class references and no longer changes the URL to a string-based route such as #/tab1.

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