This change gets rbdemo in shape for Review Board 4.0. These consist of

some changes around the structure for management commands, a change for

an app label, the removal of an argument to the flush management

command, and modern octal format support.

Tested outputting new demo fixtures from an upgraded copy of the demo

database and diffing results from what we use in production.
Tested resetting my local demo database based an demo fixtures and

verifying the results.