Integrate with opaque_keys package for checking course_ids.

Requires running Python 2.7 on clusters, since opaque keys
requires that.

* Export opaque keys and dependencies to worker instances in Hadoop.
* Support for checking if course_id is valid.
* Rudimentary support for getting course_id from URL.
* Make sure filenames from course_ids are legal, replacing characters as
  needed.
* Identify organization for each event as close to original algorithm as
  possible on existing data, but working for opaque keys as well.

Acked-by: Brian Wilson <brian@edx.org>
This will only emit more browser events for non-slashified course-ids.  Which has no impact on the past, but does going forward.  Actually it seems like a reasonable horizon to allow us to turn on other event exports, such as for workers and the like, for which a course-id might be provided that would allow us to provide more data without breaking backwards consistency.