This does two things:
1. If the TKs in the draft has changed, add/remove the corresponding
columns from the table
2. Either way, update the preview so it matches the draft text
All this only happens once you click the "Refresh" button, because
we don't want to be putting *too much* load on the app also 😜
Otherwise it throws an error because, while rendering the TK tags,
you're not allowed to have one TK come more than once. That aside,
we don't want *each* occurrence having its own table column, do we?
