Also generate certificate if only draft certificates exist
Extract params checks to before_filters

The if statement was getting too unruly to be readable.
Clean up create method

By extracting all negative responses to before filter checks.
Memoizing the creation of campaign - sorry about the :nil_but_true
Pass existing dataset through params hash to method
  (I wish ruby had decorators)
It’s the certificates published state that matters
Merge pull request #952 from theodi/feature-import-draft-existing-datasets

Create certificates for datasets with only draft certificates