Disable session timeouts for now, by default, to avoid #2792.

Fixes #2792.
Always include AttemptLogs with context_type either playlist or exercise.
Upgrade django-south from 0.7.6 to 0.8.4 (to support index_together)
Add index_together on AttemptLogs to make typical queries much faster.
Middleware to allow tastypie requests to be profiled with debug toolbar.
Merge pull request #2802 from jamalex/include_all_practice_attempts

Improved AttemptLog filter (for efficiency and correctness)
Playlist Exercise on Refresh stays on same page, now doesn't reset to first exercise
Merge branch 'nalanda-rct3' of https://github.com/learningequality/ka-lite into nalanda-rct3
Playlist Updated -- Multiplication Division Grade 4 Slug Fixed
Merge pull request #2814 from anuragkanungo/playlist_slug_fix

Playlist Updated -- Multiplication Division Grade 4 Slug Fixed
Merge pull request #2806 from anuragkanungo/playlist_refresh

#2797 - Playlist Exercise on Refresh stays on same page, now doesn't reset to first exercise
Merge pull request #2801 from jamalex/2792

Disable session timeouts for now, by default, to avoid #2792.
Merge pull request #2804 from anuragkanungo/nalanda-rct3

#2798 - Removed cell-content class which was giving dot ellipsis
Merge branch 'nalanda-rct3' of https://github.com/learningequality/ka-lite into nalanda-rct3