Added multi column layout
Added sub column support for interactive creation and editing
added grid rendering & styling of subcolumns
Fixed UI + trailing comma
Revert "added grid rendering & styling of subcolumns"

This reverts commit d8072172f4a1b3a039ba44b756279747016427bb.
Added sub column border
added sub header + css for col view configs
Use simpler type of subColumns
Merge branch 'MultiColumn-Experimental'
Fixed simple vs secondary sheet column view