Create Dataset: add support for migrating (with existing DOIs) via native API

[bmckinney]

One of the SBGrid migration requirements is to move the existing datasets, along with their DOIs, into Dataverse. Currently, it appears that this can only be done using the DDI XML import.

[pdurbin]

@bmckinney will create a new pull request to handle these two remaining items:

• Dataverse theme
• Dataset DOI

As of 4.5, one should be able to set the license via native API.