Add unseen columns to informant upon `incorporate()`

[rich-iannone]

As tables may change between uses of incorporate(), the informant currently only updates dimension values (column and row counts) but doesn’t update the columns section with the names of new columns. This should be done, perhaps updating the order of columns as well.

On top of this, some columns from a target table might be dropped or renamed over time. We need some ways to handle these changes without losing information. That’ll be a different issue though.