Expanded Series Tags API with UI

This release makes working with series tags easier. Series tags can now be created, renamed and deleted independently of any series. Series tags are no longer automatically deleted when no series are tagged with them. A UI has been added for managing series tags.

This release is the first to use the new dicom-streams dependency (cf. https://github.com/slicebox/dicom-streams), which reduces the dependencies on dcm4che throughout slicebox and continues the move towards streaming handling of dicom data everywhere.