Export data as RDSR

[Ed McDonagh]

Add function to export all or selected data as RDSR. Would require creating RDSR objects on the fly, so would need to be a potentially very long running process!

Use cases:

1. Ad-hoc or regular upload of study information to regional or national dose management system
2. Migration from OpenREM to another dose management system ( )

RDSR would need to incorporate all the information available in the database into a standards compliant RDSR - it would not be a recreation of the incoming RDSR from the original vendor.

The functionality would also need to generate RRDSR objects in the same way.

The pydicom codify function will help with generating the skeleton code for this.