Queryable student module app

Makes new tables that are queryable to get aggregate data on student per
problem information and student grades at three levels: overall course,
assignment type, and assignment.

Provides UI in instructor dashboard to view student metrics using
class_dashboard app.

Remove primary keys from queryable tables
    De-normalize user info of id, username and name into queryable tables.

Make all tests pass

* use default parameter	in get_or_create for non-unique-together
  values
* properly set module_state_key
work to factor out queryable app
more tests
yet more test work
Add metrics tab to beta dashboard.
Cleanup urls.py
add loading spinners and banner to notify instructor that loading takes a bit
Fix of unicode issue
Fix rendering issue
Fixed permission issue