New option to skip data export in Mascot searches (for Percolator)

New parameter in MascotAdapterOnline: "Mascot_server:skip_export" (true/false)
If enabled, the Mascot search is run, but the results are not exported - giving an output file (idXML) that contains only the search number, but no actual data. This can be passed on to the GenericWrapper for Mascot Percolator. The expensive export step, that is wasted if only the Percolator results are of interest, is thus saved.