Predicting a model without beam should update beam keywords

Created by: aroffringa

Beam keywords are stored with the DATA column (see #60 (closed) ). This helps enforcing / calculating the right beam at all times. However, prediction doesn't fully comply with this yet.

When predicting without the element beam, the output is already "corrected" for the element beam. Hence, the keywords should be updated to reflect that. A complicating factor is that WSClean (or other software) might be used to predict data, and in that case it would not copy the columns, so maybe there also needs to be a work-around for that.