OEC-498, Implement Oec::Queries get_edited_course_data

https://jira.ets.berkeley.edu/jira/browse/OEC-502

The diff operation will compare:
1. current Oracle data
2. edits to CSV made by department admin (e.g., instructor email addresses changed)

The OEC tool will treat "edits to CSV by dept" as data in a database. Therefore, we add get_edited_course_data method to Oec::Queries. The 'revision' argument is in anticipation of https://jira.ets.berkeley.edu/jira/browse/OEC-500 fix. Work includes changes to queries_spec
@johncrossman , could you change this to match our normal module naming (e.g., Oec::Helper)?

And out of curiosity, do you expect this one method to be called from any client other than Oec::Queries?