Enable column selection for the data viewer

[combiz]

When using the view() command with a data.frame, the data viewer does not allow for the selection of values in a single column.

Possible ways to enable this feature could include: (1) via clicking the column name (currently this triggers a column sort), (2) allow a mouse-click and vertical drag functionality without wrapping other columns in the selection, and (3) enabling the data viewer to use/launch a VSCode extension such as RainbowCSV.