Dataverse plugin: minor edits 

Indentation, function docs, header comments, variable cleanup & other minor edits from Alex's comments on pull request: https://github.com/pkp/ojs/pull/155. Will reply to his comments in a sec w/ what's fixed here & will open bug reports for the rest. 

Commits left unsquashed to distinguish code changes from spacing changes, but let me know if it should be otherwise.  Indentation issues persist until the 2nd-last commit in this series.