Attendance screen

Fixes #217.

View the commits included in this request for further details, but in short, this pull request adds an Attendance report that uses the new attendances table. Attendance records are created by the attendance page on /live_class and were refactored to use an after_save hook to create the StudentAction for the attendance.

This pull request is currently live on the staging environment for your viewing pleasure.

If all is acceptable, please let us know as a backup of the database needs to be captured before running the migration in fbe9543. That migration creates a load of new data (~17K rows) and we just want to be cautious before this gets merged in. If you have any questions, contact @iericallen or myself(@dugancathal) directly for further information.