Merge datasets

[stijn-uva]

Could be a processor that takes the URL of another dataset as a parameter; and then a new dataset is created containing the data from both the 'source' and 'target' datasets

[sal-uva]

Should datasets be from the same data source? Or do we just merge overlapping the columns and include leftovers?

I'd say it should allow both, i.e. retaining the data source type if they match, and transforming it to "custom" if not.