WIP: Extracting workflows with implicit collections from histories.
HACK: Modify contents type on index, need to remove at some point.

Need to find a way to make backbone do this.
Dataset collections - create lists and pairs via HDA multi-select.
Refactor backbone models to allow different kinds of history contents.

In particular, add a new backbone parent model (HistoryContent) refactored out of HistoryDatasetAssociation. This makes room for a forth coming HistoryDatasetCollectionAssociation model that will be emitted from the history contents API.
Refactor backbone views to allow different kinds of history contents.

This makes room for a forth coming HistoryDatasetCollectionAssociation model that will be emitted from the history contents API.
Dataset collections - backbone model.
More reworking of backbone views to allow multiple content types.
Dataset collections - backbone view.