Add query pagination

Have multiple queries. 1st loads with limit, next one does `startAfter`. Put all queries in `@activate()` array.

``` javascript
let ref = store.collection('ducks').orderBy('name', 'asc').limit(50);
let queries = [];
queries.push(ref.query());
queries.push(ref.startAfter(queries[0].content.lastObject).query());
```