mattdrayer/api-migrate-courseids: Data migration script

@chrisndodge @martynjames, here's a data migration script for converting old-style course/content identifiers to the new format.  Take a look and let me know what you think.  One thought: We might want to write-out the original values to a file in order to preserve the info in case something goes wrong during the migration.
Yea, we're going to need to be able to re-run the script over any already converted data. Good catch!