Update google analytics to include newer universal analytics

GA has been updated and has a [new API](https://developers.google.com/analytics/devguides/collection/analyticsjs/method-reference). I added the most important top-level typedefs.
This is the only way I could find to overload the return value. I tried
```typescript
get<T extends string>(fieldName: string): T;
get<T extends number>(fieldName: string): T;
get<T extends {}>(fieldName: string): T;
```
but that didn't work.