DataTable's are slow with larger data

[schloerke]

From #1637

We use shiny.render.DataTable to visual our various datasets. It appears the current design sends the entire dataframe data into the browser in a single websocket message. Where the dataframes are even moderately large with thousand of rows, it results in the browser visibly hanging. With large dataframes in the hundreds of thousands for rows, it often causes the browser to fail entirely.

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Possibly related to #1498 ?