Implement MultipleAdSizes on Android

https://developers.google.com/mobile-ads-sdk/docs/dfp/android/banner#multiple
Added missing theme on AdActivity
Update view.md
Update index.md
Removed debug and give adSizes preference over adWidth/adHeight, just as on iOS
Update app.js
Merge pull request #7 from timanrebel/feature/MultipleAdSizesAndroid

Implement MultipleAdSizes on Android