Support expanded file metadata

[djbrooke]

For files, we should support the ability to add:

• Descriptions
• Tags
• Restrictions

We should implement this in a way that is optional, as many of the sample files will not have this expanded metadata.

[landreev]

@kcondon
For testing:
If you populate a dataverse instance with the sample data collection from this branch, one of the datasets created - "Open Source at Harvard - File Hierarchy, Descriptions, Tags and Restrictions", in the "Open Source at Harvard" dataverse, will have files with extended descriptions and file category tags; and one restricted file.
It was previously not possible to have these file features automatically added by the sample data scripts. So this is what this PR does.

[pdurbin]

The datafile added in pull request #28 should be restricted, ideally, so when we pick this up we can add the proper attribute there.