Provide options to reduce data row height

[RandomFractals]

Flat UI only displays 9 and a half rows in a fixed 560px table view and each data cell sets 40px height via inline styles.

It would be more aesthetically pleasing to have shorter table data rows in applications with limited viewports, such as VSCode notebooks and their cell outputs.

I was able to overwrite some of those CSS rules, but I can't find how to remove the extra spaces between data rows:

See more info in our data table renderers: https://github.com/RandomFractals/vscode-data-table/issues/138

In general, I think it would be best to remove some of those inline div styles and add more custom classes for the table rows and cells.