now generate user usage logs.
add version not just to fields, but also to models.
this only works when we increment the version :)
None === no limit.  adding TODO
Merge pull request #188 from bcipolli/persist_syncsessions

Keep a minimum number of sync session logs on the client, for future use in stats display.
Merge pull request #187 from bcipolli/python26_cleanup

Python26 cleanup
Merge branch 'user_activity_logs' of git://github.com/bcipolli/ka-lite into bcipolli-user_activity_logs
Merge remote-tracking branch 'origin/user_logs_syncing' into control_panel
Merge remote-tracking branch 'upstream/develop' into control_panel