Pagination Improvements

[chriswhong]

Let's spend some time making pagination of tabular datasets more joyful.

• Sticky row numbers (scrolling to the right, I should still see row numbers
• Refactor pagination store to use limit/offset
• Bug: JSON double body fetch (to repro: switch to a JSON dataset, you will see 50 rows, then 100 rows loaded)
• Lazy loading (anticipate y scrolling, fetch data before user gets to the end)