WIP: Feat selections#145

Draft

maartenbreddels wants to merge 2 commits intojupyter-widgets-contrib:masterfrom

maartenbreddels:feat_selections

Commits on Sep 24, 2019

feat: highlight selected rows, columns or both
maartenbreddels
committed
fix(css): change selection color and opacity to have better visibility in dark theme
maartenbreddels
committed