Change double column detection

I had some problems with two money column detection (see test). I solved this by making a special method for evaluating that will accept the new merged column if the money_score is higher than the old columns.

Another approach would be to check whether at any row only one of the columns has a value, since that would be a strong indication of two columns. This would need more in depth changes though, so I decided to take this simpler/less intrusive approach.