Function to load a set from collection files
Can optionally set the set name as a genre in the returned table.
loadSets() returns table of all defined collections (and the
number of plays in each).
loadSet(setName, addGenreColumn = FALSE)
A character vector. The name of the set(s) to retrieve.
Logical. Whether to set the Genre-column in the returned table to the set name. If set to FALSE (default), a vector is returned. In this case, association to collections is not returned. Otherwise, it's a data.frame.
A character vector with play ids that belong to the set.