SS: re-send old submissions to RWS when active dataset changes

- We only send results for the active dataset to RWS.
- We also now re-send all results for a task when the dataset is changed.
cmstestsuite: update to manage Datasets

We don't actually test datasets, but just put everything into the default
dataset.
SpoolExporter: update to manage Datasets
YamlLoader: update to manage Datasets
YamlReimporter: update to manage Datasets