ExtractorCLI should not block specifying Modality when doing Series level extractions

[tznind]

Also the ExtractorCLI tool blocks extractions with modality specified unless you pass it StudyInstanceUIDs... need to remember if there's a specific reason for that check being there

@rkm

I believe the logic was: Studies have multiple modalities but Series are only a single Modality. So when you get a PT,CT combo scan then there should be a Series for the PT and a different one for the CT. So the idea was that you would only really need to specify a Modality when you are specifying a Study level extraction

I suspect that logic is flawed though, I seem to remember hearing about SR images being tacked onto the end of existing Series with the same SeriesInstanceUID as the rest of the extraction. Either way we shouldnt be blocking specifying Modality as it reduces the number of tables we have to query.