Allow batch additions to DSO data pool

Currently, to add listings to a DSO data pool (solidarity economy, for example), it has to be done one-by-one (unless imported from file). It would be great to have (minimally) a button like "add all search results to DSO data pool." Perhaps the ideal would be to also allow a pool editor to check boxes next to a list of search results to select (or unselect) specific entries for inclusion.