Column selection via checkbox and radio items

[chriddyp]

Similarly to how row selection works

[chriddyp]

What this UI could look like:

[Marc-Andre-Rivet]

Discussion notes: Add a column_selectable prop at the table level that is similar to row_selectable + add a nested prop to columns that has the same type as deletable and will toggle whether a specific column header is selectable or not. To be improved in #495.