Add versioning for datasets

[phebal]

Datasets currently can be associated with any number of distributions. We want to to be able to create dataset + distribution pairs that we could 'freeze' (not allow edits) and version. Any edit would result in a new version. The ultimate goal is to be able to mint DOIs for dataset-distribution pairs.

• Allow creation of fixed Dataset + [Distribuitions] sets (collections?) that can be frozen
• You can edit the Dataset in a set but not the associated distribution
• You can mint a DOI for the set Add DOI minting for dataset-distro sets #18
• Version the Dataset associated with the set (optional and might be annoying to implement)
• Create a GUI that will allow DOI minting. Ask user to chose the dataset and the associated distributions and inform them that they won't be able to change the association once the set is created and DOI minted.