Allow mutating the columns

[severo]

When adding a new column, the whole table is recreated.

add_column_scroll.mp4

See the story in this branch: story-add-column

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Instead, we want to allow mutating the columns (add/delete/reorder at least), and update the table smoothly.

[severo]

Possibly, this means adding an event to inform the columns in the dataframe have been updated.

related issues: #223, #297, #2