Return unicode strings from models.

Issue #225.
Update troubleshooting steps.

Issue #219.
Foursquare: Add API tester.
Untappd: Attach Foursquare venue if available.

Issue #178.
Foursquare: attach photos when available.

Issue #143.
Show highlight photo in single-photo sessions.

Closes #248.
Embed SSO urls when available.
Abstract authentication backend.
Cleanup: Drop unnecessary fields in User model.
Cleanup: Drop sites framework.
Flatten statistics.
Remove session chunks.

Originally these served as caches of per-session,
per-user, and per-keg volume statistics, roles now
served by the multi-view Stats table.
Cleanup: Drinks always require a keg.
Cleanup: Remove sound server, temporarily.

It had bitrotted, and should return as a plugin.
Add email_user to User model, for compatibility with Django.

Missed in 8a058f5.
Cleanup: Remove stale apps.

- registration: we use our own registration profile
  and views.
- socialregistration: social sign-in was dropped a while
  ago.
Bump foursquare dependency.

Issue #143.
Update summarize_drinkers.
Add keg_ids.
setup: Don't create a default controller.

Issue #247.