Check dataset

@kaiec @Dommii

I put in a method call to a function that resolves the input string to a file/directory/oai-pmh address, retrieves the first file (for dirs/oai-pmh), does XSLT transformation if necessary, loads the resulting model, retrieves the first CHO, parses the dataset from that URI and if that dataset doesn't match the dataset defined by the ingestion configuration, throws a ValidationError.