Add necessary elements for exercise summary generation

Summary:
Includes modification to ka_hive_init.q to include new summary table
as well as daily_report.json to export reports to mongo

Test Plan: Execute the queries specified in the exercise_summary.q and relevant parts of ka_hive_init.q

Reviewers: jace

Reviewed By: jace

Differential Revision: http://phabricator.khanacademy.org/D2159