Support for endless scrolling / load more

As an alternative to paging, users may want to use a "Load More" button or endless scrolling.

This could possibly an action that looks something like:

```
loadMore(20)
```

It would use the paging API to fetch the next page, but append the new results to the current results. It could also potentially be an option to the existing paging action that simply appends rather than replacing the results.

Start by reading the existing paging API and the proposed loadMore(20) action. Determine how the next page is fetched and how results are currently replaced, then define whether loading more is a separate action or an option on paging. Done means subsequent pages are fetched and appended without losing the current results.

Written by the indexing model from the issue text.