In SRA conversion, submission.xml missing broker name

Looks like in the SRA converter, the submission.xml file produced in conversions does not enter the `broker_name` attribute in the `<SUBMISSION>` element. This happens when trying it out on both BII-S-3 and BII-S-7 datasets, where `Comment[SRA Broker Name]` is present and has some value set, yet it does not appear in the exported SRA.
