Merge pull request #2650 from learningequality/nalanda-rct3

Nalanda rct3 release
Merge pull request #2725 from anuragkanungo/nalanda-rct3

Updated Playlists -- Added Pre-requisite and advanced playlists
Increase tastypie limits for CSV export to make them unlimited.
Tweak to facility unit test mapping.
Added timestamp_first and timestamp_last to exercise log export.
Convenience method on ExerciseLog to get AttemptLogs.
Adds is_teacher field to all relevant CSV exports.
Adds timestamp_first and timestamp_last fields to TestLog export.
Merge pull request #2739 from jamalex/exercise_data_export_fixes

Exercise data export fixes
Playlists Updated -- Grade 5,6 Advanced Playlists now visible
Advanced Playlists moved to unit 0
Delete duplicate exercises from playlists.
Merge pull request #2740 from jamalex/fix_playlists

Fix playlists