Row virtualisation is not optimal

When I scroll the grid past the end of the virtualised rows, the virtualisation is updated and all rows' data is rebound to new DOM elements.

For example, I have a 30 row grid. I scroll down 3 rows, no DOM activity as that's within the virtualisation buffers. I scroll a bit more, and then all 30 DOM row elements are rebound to new data elements.

This makes it particularly expensive to scroll a grid with non-trivial data e.g. sparkline charts in a column.

It seems that it would be more efficient to preserve the already rendered rows in this case, dispose of those going off the top, and add new ones at the bottom.