Add Flat Data Grid renderer

[RandomFractals]

see: https://github.com/githubocto/flat-ui

[RandomFractals]

might need to fiddle with built-in vscode styles to make it look better in the dark UI theme:

[RandomFractals]

finalized flat data grid UI:

Note: flat UI styles are hard to change for the dark theme. So, we'll stick with the white grid background for now.

[RandomFractals]

updated grid display with number of columns display added in githubocto/flat-ui#26: