Update Dataverse API to use persistent File ids instead of db file ids

[raprasad]

update form and API: http://metadata.2ravens.org/preprocess/dataverse-form

[raprasad]

retrieve files by persistent id: http://guides.dataverse.org/en/latest/api/dataaccess.html#basic-file-access

[raprasad]

Make changes to accept the new persistentId for files:

• https://dataverse.harvard.edu/file.xhtml?persistentId=doi:10.7910/DVN/RQOZIJ/AUPVMH

Changes:

1. DataverseFileInfo model
   • add a persistent_id field
   • set the datafile_id default to -1
   • update Meta
     • unique_together list should also include persistent_id
   • update get_file_access_url
     • Return the url for persistent_id, if that's not available, return the url for datafile_id
   • update get_file_page_url
     • Similar to above, try using persistent_id first
2. URLHelper (in url_helper.py)
   • add get_persistent_id_from_url method
     • follow the format of URLHelper.get_datafile_id_from_url
3. DataverseFileRetriever.load_dataverse_info
   • update this to work with persistent_id or file_id
     • May need to make new methods--e.g. if it's persistent_id, do one thing, use another method for file_id
4. citation_retriever.py
   • This one may be a bit harder
   • See if call_search_api_for_doi can be called with a persistentId
     • Use this forum if you have questions: https://groups.google.com/forum/#!forum/dataverse-community