Cursor-based pagination

[Kos]

The code assumes a lot about page numbers - that they are integers and the initial page is 1.

When possible, the page number should be treated as an opaque identifier, so that you can paginate using cursors as well as page numbers. Page numbers shouldn't be generally produced by RTable, only taken from incoming DataResponses.

However, we'd still want to allow extra features that base on numerical pages, like "showing page 5 of 123" or "go to page 5". This might mean that RTable would have a separate mode for numerical and opaque page identifiers. Or we could just look at DataResponse and decide what to show (as in, if we have count and the page identifier is numeric, then assume sequential pages)